OSCL-LXR linux-6.0.1/​drivers/​hwtracing/​stm/​core.c	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * System Trace Module (STM) infrastructure
  * Copyright (c) 2014, Intel Corporation.
  *
  * STM class implements generic infrastructure for  System Trace Module devices
  * as defined in MIPI STPv2 specification.
  */
 
 #include <linux/pm_runtime.h>
 #include <linux/uaccess.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/compat.h>
 #include <linux/kdev_t.h>
 #include <linux/srcu.h>
 #include <linux/slab.h>
 #include <linux/stm.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/vmalloc.h>
 #include "stm.h"
 
 #include <uapi/linux/stm.h>
 
 static unsigned int stm_core_up;
 
 /*
  * The SRCU here makes sure that STM device doesn't disappear from under a
  * stm_source_write() caller, which may want to have as little overhead as
  * possible.
  */
 static struct srcu_struct stm_source_srcu;
 
 static ssize_t masters_show(struct device *dev,
                 struct device_attribute *attr,
                 char *buf)
 {
     struct stm_device *stm = to_stm_device(dev);
     int ret;
 
     ret = sprintf(buf, "%u %u\n", stm->data->sw_start, stm->data->sw_end);
 
     return ret;
 }
 
 static DEVICE_ATTR_RO(masters);
 
 static ssize_t channels_show(struct device *dev,
                  struct device_attribute *attr,
                  char *buf)
 {
     struct stm_device *stm = to_stm_device(dev);
     int ret;
 
     ret = sprintf(buf, "%u\n", stm->data->sw_nchannels);
 
     return ret;
 }
 
 static DEVICE_ATTR_RO(channels);
 
 static ssize_t hw_override_show(struct device *dev,
                 struct device_attribute *attr,
                 char *buf)
 {
     struct stm_device *stm = to_stm_device(dev);
     int ret;
 
     ret = sprintf(buf, "%u\n", stm->data->hw_override);
 
     return ret;
 }
 
 static DEVICE_ATTR_RO(hw_override);
 
 static struct attribute *stm_attrs[] = {
     &dev_attr_masters.attr,
     &dev_attr_channels.attr,
     &dev_attr_hw_override.attr,
     NULL,
 };
 
 ATTRIBUTE_GROUPS(stm);
 
 static struct class stm_class = {
     .name       = "stm",
     .dev_groups = stm_groups,
 };
 
 /**
  * stm_find_device() - find stm device by name
  * @buf:    character buffer containing the name
  *
  * This is called when either policy gets assigned to an stm device or an
  * stm_source device gets linked to an stm device.
  *
  * This grabs device's reference (get_device()) and module reference, both
  * of which the calling path needs to make sure to drop with stm_put_device().
  *
  * Return:  stm device pointer or null if lookup failed.
  */
 struct stm_device *stm_find_device(const char *buf)
 {
     struct stm_device *stm;
     struct device *dev;
 
     if (!stm_core_up)
         return NULL;
 
     dev = class_find_device_by_name(&stm_class, buf);
     if (!dev)
         return NULL;
 
     stm = to_stm_device(dev);
     if (!try_module_get(stm->owner)) {
         /* matches class_find_device() above */
         put_device(dev);
         return NULL;
     }
 
     return stm;
 }
 
 /**
  * stm_put_device() - drop references on the stm device
  * @stm:    stm device, previously acquired by stm_find_device()
  *
  * This drops the module reference and device reference taken by
  * stm_find_device() or stm_char_open().
  */
 void stm_put_device(struct stm_device *stm)
 {
     module_put(stm->owner);
     put_device(&stm->dev);
 }
 
 /*
  * Internally we only care about software-writable masters here, that is the
  * ones in the range [stm_data->sw_start..stm_data..sw_end], however we need
  * original master numbers to be visible externally, since they are the ones
  * that will appear in the STP stream. Thus, the internal bookkeeping uses
  * $master - stm_data->sw_start to reference master descriptors and such.
  */
 
 #define __stm_master(_s, _m)                \
     ((_s)->masters[(_m) - (_s)->data->sw_start])
 
 static inline struct stp_master *
 stm_master(struct stm_device *stm, unsigned int idx)
 {
     if (idx < stm->data->sw_start || idx > stm->data->sw_end)
         return NULL;
 
     return __stm_master(stm, idx);
 }
 
 static int stp_master_alloc(struct stm_device *stm, unsigned int idx)
 {
     struct stp_master *master;
 
     master = kzalloc(struct_size(master, chan_map,
                      BITS_TO_LONGS(stm->data->sw_nchannels)),
              GFP_ATOMIC);
     if (!master)
         return -ENOMEM;
 
     master->nr_free = stm->data->sw_nchannels;
     __stm_master(stm, idx) = master;
 
     return 0;
 }
 
 static void stp_master_free(struct stm_device *stm, unsigned int idx)
 {
     struct stp_master *master = stm_master(stm, idx);
 
     if (!master)
         return;
 
     __stm_master(stm, idx) = NULL;
     kfree(master);
 }
 
 static void stm_output_claim(struct stm_device *stm, struct stm_output *output)
 {
     struct stp_master *master = stm_master(stm, output->master);
 
     lockdep_assert_held(&stm->mc_lock);
     lockdep_assert_held(&output->lock);
 
     if (WARN_ON_ONCE(master->nr_free < output->nr_chans))
         return;
 
     bitmap_allocate_region(&master->chan_map[0], output->channel,
                    ilog2(output->nr_chans));
 
     master->nr_free -= output->nr_chans;
 }
 
 static void
 stm_output_disclaim(struct stm_device *stm, struct stm_output *output)
 {
     struct stp_master *master = stm_master(stm, output->master);
 
     lockdep_assert_held(&stm->mc_lock);
     lockdep_assert_held(&output->lock);
 
     bitmap_release_region(&master->chan_map[0], output->channel,
                   ilog2(output->nr_chans));
 
     master->nr_free += output->nr_chans;
     output->nr_chans = 0;
 }
 
 /*
  * This is like bitmap_find_free_region(), except it can ignore @start bits
  * at the beginning.
  */
 static int find_free_channels(unsigned long *bitmap, unsigned int start,
                   unsigned int end, unsigned int width)
 {
     unsigned int pos;
     int i;
 
     for (pos = start; pos < end + 1; pos = ALIGN(pos, width)) {
         pos = find_next_zero_bit(bitmap, end + 1, pos);
         if (pos + width > end + 1)
             break;
 
         if (pos & (width - 1))
             continue;
 
         for (i = 1; i < width && !test_bit(pos + i, bitmap); i++)
             ;
         if (i == width)
             return pos;
 
         /* step over [pos..pos+i) to continue search */
         pos += i;
     }
 
     return -1;
 }
 
 static int
 stm_find_master_chan(struct stm_device *stm, unsigned int width,
              unsigned int *mstart, unsigned int mend,
              unsigned int *cstart, unsigned int cend)
 {
     struct stp_master *master;
     unsigned int midx;
     int pos, err;
 
     for (midx = *mstart; midx <= mend; midx++) {
         if (!stm_master(stm, midx)) {
             err = stp_master_alloc(stm, midx);
             if (err)
                 return err;
         }
 
         master = stm_master(stm, midx);
 
         if (!master->nr_free)
             continue;
 
         pos = find_free_channels(master->chan_map, *cstart, cend,
                      width);
         if (pos < 0)
             continue;
 
         *mstart = midx;
         *cstart = pos;
         return 0;
     }
 
     return -ENOSPC;
 }
 
 static int stm_output_assign(struct stm_device *stm, unsigned int width,
                  struct stp_policy_node *policy_node,
                  struct stm_output *output)
 {
     unsigned int midx, cidx, mend, cend;
     int ret = -EINVAL;
 
     if (width > stm->data->sw_nchannels)
         return -EINVAL;
 
     /* We no longer accept policy_node==NULL here */
     if (WARN_ON_ONCE(!policy_node))
         return -EINVAL;
 
     /*
      * Also, the caller holds reference to policy_node, so it won't
      * disappear on us.
      */
     stp_policy_node_get_ranges(policy_node, &midx, &mend, &cidx, &cend);
 
     spin_lock(&stm->mc_lock);
     spin_lock(&output->lock);
     /* output is already assigned -- shouldn't happen */
     if (WARN_ON_ONCE(output->nr_chans))
         goto unlock;
 
     ret = stm_find_master_chan(stm, width, &midx, mend, &cidx, cend);
     if (ret < 0)
         goto unlock;
 
     output->master = midx;
     output->channel = cidx;
     output->nr_chans = width;
     if (stm->pdrv->output_open) {
         void *priv = stp_policy_node_priv(policy_node);
 
         if (WARN_ON_ONCE(!priv))
             goto unlock;
 
         /* configfs subsys mutex is held by the caller */
         ret = stm->pdrv->output_open(priv, output);
         if (ret)
             goto unlock;
     }
 
     stm_output_claim(stm, output);
     dev_dbg(&stm->dev, "assigned %u:%u (+%u)\n", midx, cidx, width);
 
     ret = 0;
 unlock:
     if (ret)
         output->nr_chans = 0;
 
     spin_unlock(&output->lock);
     spin_unlock(&stm->mc_lock);
 
     return ret;
 }
 
 static void stm_output_free(struct stm_device *stm, struct stm_output *output)
 {
     spin_lock(&stm->mc_lock);
     spin_lock(&output->lock);
     if (output->nr_chans)
         stm_output_disclaim(stm, output);
     if (stm->pdrv && stm->pdrv->output_close)
         stm->pdrv->output_close(output);
     spin_unlock(&output->lock);
     spin_unlock(&stm->mc_lock);
 }
 
 static void stm_output_init(struct stm_output *output)
 {
     spin_lock_init(&output->lock);
 }
 
 static int major_match(struct device *dev, const void *data)
 {
     unsigned int major = *(unsigned int *)data;
 
     return MAJOR(dev->devt) == major;
 }
 
 /*
  * Framing protocol management
  * Modules can implement STM protocol drivers and (un-)register them
  * with the STM class framework.
  */
 static struct list_head stm_pdrv_head;
 static struct mutex stm_pdrv_mutex;
 
 struct stm_pdrv_entry {
     struct list_head            entry;
     const struct stm_protocol_driver    *pdrv;
     const struct config_item_type       *node_type;
 };
 
 static const struct stm_pdrv_entry *
 __stm_lookup_protocol(const char *name)
 {
     struct stm_pdrv_entry *pe;
 
     /*
      * If no name is given (NULL or ""), fall back to "p_basic".
      */
     if (!name || !*name)
         name = "p_basic";
 
     list_for_each_entry(pe, &stm_pdrv_head, entry) {
         if (!strcmp(name, pe->pdrv->name))
             return pe;
     }
 
     return NULL;
 }
 
 int stm_register_protocol(const struct stm_protocol_driver *pdrv)
 {
     struct stm_pdrv_entry *pe = NULL;
     int ret = -ENOMEM;
 
     mutex_lock(&stm_pdrv_mutex);
 
     if (__stm_lookup_protocol(pdrv->name)) {
         ret = -EEXIST;
         goto unlock;
     }
 
     pe = kzalloc(sizeof(*pe), GFP_KERNEL);
     if (!pe)
         goto unlock;
 
     if (pdrv->policy_attr) {
         pe->node_type = get_policy_node_type(pdrv->policy_attr);
         if (!pe->node_type)
             goto unlock;
     }
 
     list_add_tail(&pe->entry, &stm_pdrv_head);
     pe->pdrv = pdrv;
 
     ret = 0;
 unlock:
     mutex_unlock(&stm_pdrv_mutex);
 
     if (ret)
         kfree(pe);
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(stm_register_protocol);
 
 void stm_unregister_protocol(const struct stm_protocol_driver *pdrv)
 {
     struct stm_pdrv_entry *pe, *iter;
 
     mutex_lock(&stm_pdrv_mutex);
 
     list_for_each_entry_safe(pe, iter, &stm_pdrv_head, entry) {
         if (pe->pdrv == pdrv) {
             list_del(&pe->entry);
 
             if (pe->node_type) {
                 kfree(pe->node_type->ct_attrs);
                 kfree(pe->node_type);
             }
             kfree(pe);
             break;
         }
     }
 
     mutex_unlock(&stm_pdrv_mutex);
 }
 EXPORT_SYMBOL_GPL(stm_unregister_protocol);
 
 static bool stm_get_protocol(const struct stm_protocol_driver *pdrv)
 {
     return try_module_get(pdrv->owner);
 }
 
 void stm_put_protocol(const struct stm_protocol_driver *pdrv)
 {
     module_put(pdrv->owner);
 }
 
 int stm_lookup_protocol(const char *name,
             const struct stm_protocol_driver **pdrv,
             const struct config_item_type **node_type)
 {
     const struct stm_pdrv_entry *pe;
 
     mutex_lock(&stm_pdrv_mutex);
 
     pe = __stm_lookup_protocol(name);
     if (pe && pe->pdrv && stm_get_protocol(pe->pdrv)) {
         *pdrv = pe->pdrv;
         *node_type = pe->node_type;
     }
 
     mutex_unlock(&stm_pdrv_mutex);
 
     return pe ? 0 : -ENOENT;
 }
 
 static int stm_char_open(struct inode *inode, struct file *file)
 {
     struct stm_file *stmf;
     struct device *dev;
     unsigned int major = imajor(inode);
     int err = -ENOMEM;
 
     dev = class_find_device(&stm_class, NULL, &major, major_match);
     if (!dev)
         return -ENODEV;
 
     stmf = kzalloc(sizeof(*stmf), GFP_KERNEL);
     if (!stmf)
         goto err_put_device;
 
     err = -ENODEV;
     stm_output_init(&stmf->output);
     stmf->stm = to_stm_device(dev);
 
     if (!try_module_get(stmf->stm->owner))
         goto err_free;
 
     file->private_data = stmf;
 
     return nonseekable_open(inode, file);
 
 err_free:
     kfree(stmf);
 err_put_device:
     /* matches class_find_device() above */
     put_device(dev);
 
     return err;
 }
 
 static int stm_char_release(struct inode *inode, struct file *file)
 {
     struct stm_file *stmf = file->private_data;
     struct stm_device *stm = stmf->stm;
 
     if (stm->data->unlink)
         stm->data->unlink(stm->data, stmf->output.master,
                   stmf->output.channel);
 
     stm_output_free(stm, &stmf->output);
 
     /*
      * matches the stm_char_open()'s
      * class_find_device() + try_module_get()
      */
     stm_put_device(stm);
     kfree(stmf);
 
     return 0;
 }
 
 static int
 stm_assign_first_policy(struct stm_device *stm, struct stm_output *output,
             char **ids, unsigned int width)
 {
     struct stp_policy_node *pn;
     int err, n;
 
     /*
      * On success, stp_policy_node_lookup() will return holding the
      * configfs subsystem mutex, which is then released in
      * stp_policy_node_put(). This allows the pdrv->output_open() in
      * stm_output_assign() to serialize against the attribute accessors.
      */
     for (n = 0, pn = NULL; ids[n] && !pn; n++)
         pn = stp_policy_node_lookup(stm, ids[n]);
 
     if (!pn)
         return -EINVAL;
 
     err = stm_output_assign(stm, width, pn, output);
 
     stp_policy_node_put(pn);
 
     return err;
 }
 
 /**
  * stm_data_write() - send the given payload as data packets
  * @data:   stm driver's data
  * @m:      STP master
  * @c:      STP channel
  * @ts_first:   timestamp the first packet
  * @buf:    data payload buffer
  * @count:  data payload size
  */
 ssize_t notrace stm_data_write(struct stm_data *data, unsigned int m,
                    unsigned int c, bool ts_first, const void *buf,
                    size_t count)
 {
     unsigned int flags = ts_first ? STP_PACKET_TIMESTAMPED : 0;
     ssize_t sz;
     size_t pos;
 
     for (pos = 0, sz = 0; pos < count; pos += sz) {
         sz = min_t(unsigned int, count - pos, 8);
         sz = data->packet(data, m, c, STP_PACKET_DATA, flags, sz,
                   &((u8 *)buf)[pos]);
         if (sz <= 0)
             break;
 
         if (ts_first) {
             flags = 0;
             ts_first = false;
         }
     }
 
     return sz < 0 ? sz : pos;
 }
 EXPORT_SYMBOL_GPL(stm_data_write);
 
 static ssize_t notrace
 stm_write(struct stm_device *stm, struct stm_output *output,
       unsigned int chan, const char *buf, size_t count)
 {
     int err;
 
     /* stm->pdrv is serialized against policy_mutex */
     if (!stm->pdrv)
         return -ENODEV;
 
     err = stm->pdrv->write(stm->data, output, chan, buf, count);
     if (err < 0)
         return err;
 
     return err;
 }
 
 static ssize_t stm_char_write(struct file *file, const char __user *buf,
                   size_t count, loff_t *ppos)
 {
     struct stm_file *stmf = file->private_data;
     struct stm_device *stm = stmf->stm;
     char *kbuf;
     int err;
 
     if (count + 1 > PAGE_SIZE)
         count = PAGE_SIZE - 1;
 
     /*
      * If no m/c have been assigned to this writer up to this
      * point, try to use the task name and "default" policy entries.
      */
     if (!stmf->output.nr_chans) {
         char comm[sizeof(current->comm)];
         char *ids[] = { comm, "default", NULL };
 
         get_task_comm(comm, current);
 
         err = stm_assign_first_policy(stmf->stm, &stmf->output, ids, 1);
         /*
          * EBUSY means that somebody else just assigned this
          * output, which is just fine for write()
          */
         if (err)
             return err;
     }
 
     kbuf = kmalloc(count + 1, GFP_KERNEL);
     if (!kbuf)
         return -ENOMEM;
 
     err = copy_from_user(kbuf, buf, count);
     if (err) {
         kfree(kbuf);
         return -EFAULT;
     }
 
     pm_runtime_get_sync(&stm->dev);
 
     count = stm_write(stm, &stmf->output, 0, kbuf, count);
 
     pm_runtime_mark_last_busy(&stm->dev);
     pm_runtime_put_autosuspend(&stm->dev);
     kfree(kbuf);
 
     return count;
 }
 
 static void stm_mmap_open(struct vm_area_struct *vma)
 {
     struct stm_file *stmf = vma->vm_file->private_data;
     struct stm_device *stm = stmf->stm;
 
     pm_runtime_get(&stm->dev);
 }
 
 static void stm_mmap_close(struct vm_area_struct *vma)
 {
     struct stm_file *stmf = vma->vm_file->private_data;
     struct stm_device *stm = stmf->stm;
 
     pm_runtime_mark_last_busy(&stm->dev);
     pm_runtime_put_autosuspend(&stm->dev);
 }
 
 static const struct vm_operations_struct stm_mmap_vmops = {
     .open   = stm_mmap_open,
     .close  = stm_mmap_close,
 };
 
 static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
 {
     struct stm_file *stmf = file->private_data;
     struct stm_device *stm = stmf->stm;
     unsigned long size, phys;
 
     if (!stm->data->mmio_addr)
         return -EOPNOTSUPP;
 
     if (vma->vm_pgoff)
         return -EINVAL;
 
     size = vma->vm_end - vma->vm_start;
 
     if (stmf->output.nr_chans * stm->data->sw_mmiosz != size)
         return -EINVAL;
 
     phys = stm->data->mmio_addr(stm->data, stmf->output.master,
                     stmf->output.channel,
                     stmf->output.nr_chans);
 
     if (!phys)
         return -EINVAL;
 
     pm_runtime_get_sync(&stm->dev);
 
     vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
     vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
     vma->vm_ops = &stm_mmap_vmops;
     vm_iomap_memory(vma, phys, size);
 
     return 0;
 }
 
 static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
 {
     struct stm_device *stm = stmf->stm;
     struct stp_policy_id *id;
     char *ids[] = { NULL, NULL };
     int ret = -EINVAL, wlimit = 1;
     u32 size;
 
     if (stmf->output.nr_chans)
         return -EBUSY;
 
     if (copy_from_user(&size, arg, sizeof(size)))
         return -EFAULT;
 
     if (size < sizeof(*id) || size >= PATH_MAX + sizeof(*id))
         return -EINVAL;
 
     /*
      * size + 1 to make sure the .id string at the bottom is terminated,
      * which is also why memdup_user() is not useful here
      */
     id = kzalloc(size + 1, GFP_KERNEL);
     if (!id)
         return -ENOMEM;
 
     if (copy_from_user(id, arg, size)) {
         ret = -EFAULT;
         goto err_free;
     }
 
     if (id->__reserved_0 || id->__reserved_1)
         goto err_free;
 
     if (stm->data->sw_mmiosz)
         wlimit = PAGE_SIZE / stm->data->sw_mmiosz;
 
     if (id->width < 1 || id->width > wlimit)
         goto err_free;
 
     ids[0] = id->id;
     ret = stm_assign_first_policy(stmf->stm, &stmf->output, ids,
                       id->width);
     if (ret)
         goto err_free;
 
     if (stm->data->link)
         ret = stm->data->link(stm->data, stmf->output.master,
                       stmf->output.channel);
 
     if (ret)
         stm_output_free(stmf->stm, &stmf->output);
 
 err_free:
     kfree(id);
 
     return ret;
 }
 
 static int stm_char_policy_get_ioctl(struct stm_file *stmf, void __user *arg)
 {
     struct stp_policy_id id = {
         .size       = sizeof(id),
         .master     = stmf->output.master,
         .channel    = stmf->output.channel,
         .width      = stmf->output.nr_chans,
         .__reserved_0   = 0,
         .__reserved_1   = 0,
     };
 
     return copy_to_user(arg, &id, id.size) ? -EFAULT : 0;
 }
 
 static long
 stm_char_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
     struct stm_file *stmf = file->private_data;
     struct stm_data *stm_data = stmf->stm->data;
     int err = -ENOTTY;
     u64 options;
 
     switch (cmd) {
     case STP_POLICY_ID_SET:
         err = stm_char_policy_set_ioctl(stmf, (void __user *)arg);
         if (err)
             return err;
 
         return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
 
     case STP_POLICY_ID_GET:
         return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
 
     case STP_SET_OPTIONS:
         if (copy_from_user(&options, (u64 __user *)arg, sizeof(u64)))
             return -EFAULT;
 
         if (stm_data->set_options)
             err = stm_data->set_options(stm_data,
                             stmf->output.master,
                             stmf->output.channel,
                             stmf->output.nr_chans,
                             options);
 
         break;
     default:
         break;
     }
 
     return err;
 }
 
 static const struct file_operations stm_fops = {
     .open       = stm_char_open,
     .release    = stm_char_release,
     .write      = stm_char_write,
     .mmap       = stm_char_mmap,
     .unlocked_ioctl = stm_char_ioctl,
     .compat_ioctl   = compat_ptr_ioctl,
     .llseek     = no_llseek,
 };
 
 static void stm_device_release(struct device *dev)
 {
     struct stm_device *stm = to_stm_device(dev);
 
     vfree(stm);
 }
 
 int stm_register_device(struct device *parent, struct stm_data *stm_data,
             struct module *owner)
 {
     struct stm_device *stm;
     unsigned int nmasters;
     int err = -ENOMEM;
 
     if (!stm_core_up)
         return -EPROBE_DEFER;
 
     if (!stm_data->packet || !stm_data->sw_nchannels)
         return -EINVAL;
 
     nmasters = stm_data->sw_end - stm_data->sw_start + 1;
     stm = vzalloc(sizeof(*stm) + nmasters * sizeof(void *));
     if (!stm)
         return -ENOMEM;
 
     stm->major = register_chrdev(0, stm_data->name, &stm_fops);
     if (stm->major < 0)
         goto err_free;
 
     device_initialize(&stm->dev);
     stm->dev.devt = MKDEV(stm->major, 0);
     stm->dev.class = &stm_class;
     stm->dev.parent = parent;
     stm->dev.release = stm_device_release;
 
     mutex_init(&stm->link_mutex);
     spin_lock_init(&stm->link_lock);
     INIT_LIST_HEAD(&stm->link_list);
 
     /* initialize the object before it is accessible via sysfs */
     spin_lock_init(&stm->mc_lock);
     mutex_init(&stm->policy_mutex);
     stm->sw_nmasters = nmasters;
     stm->owner = owner;
     stm->data = stm_data;
     stm_data->stm = stm;
 
     err = kobject_set_name(&stm->dev.kobj, "%s", stm_data->name);
     if (err)
         goto err_device;
 
     err = device_add(&stm->dev);
     if (err)
         goto err_device;
 
     /*
      * Use delayed autosuspend to avoid bouncing back and forth
      * on recurring character device writes, with the initial
      * delay time of 2 seconds.
      */
     pm_runtime_no_callbacks(&stm->dev);
     pm_runtime_use_autosuspend(&stm->dev);
     pm_runtime_set_autosuspend_delay(&stm->dev, 2000);
     pm_runtime_set_suspended(&stm->dev);
     pm_runtime_enable(&stm->dev);
 
     return 0;
 
 err_device:
     unregister_chrdev(stm->major, stm_data->name);
 
     /* matches device_initialize() above */
     put_device(&stm->dev);
 err_free:
     vfree(stm);
 
     return err;
 }
 EXPORT_SYMBOL_GPL(stm_register_device);
 
 static int __stm_source_link_drop(struct stm_source_device *src,
                   struct stm_device *stm);
 
 void stm_unregister_device(struct stm_data *stm_data)
 {
     struct stm_device *stm = stm_data->stm;
     struct stm_source_device *src, *iter;
     int i, ret;
 
     pm_runtime_dont_use_autosuspend(&stm->dev);
     pm_runtime_disable(&stm->dev);
 
     mutex_lock(&stm->link_mutex);
     list_for_each_entry_safe(src, iter, &stm->link_list, link_entry) {
         ret = __stm_source_link_drop(src, stm);
         /*
          * src <-> stm link must not change under the same
          * stm::link_mutex, so complain loudly if it has;
          * also in this situation ret!=0 means this src is
          * not connected to this stm and it should be otherwise
          * safe to proceed with the tear-down of stm.
          */
         WARN_ON_ONCE(ret);
     }
     mutex_unlock(&stm->link_mutex);
 
     synchronize_srcu(&stm_source_srcu);
 
     unregister_chrdev(stm->major, stm_data->name);
 
     mutex_lock(&stm->policy_mutex);
     if (stm->policy)
         stp_policy_unbind(stm->policy);
     mutex_unlock(&stm->policy_mutex);
 
     for (i = stm->data->sw_start; i <= stm->data->sw_end; i++)
         stp_master_free(stm, i);
 
     device_unregister(&stm->dev);
     stm_data->stm = NULL;
 }
 EXPORT_SYMBOL_GPL(stm_unregister_device);
 
 /*
  * stm::link_list access serialization uses a spinlock and a mutex; holding
  * either of them guarantees that the list is stable; modification requires
  * holding both of them.
  *
  * Lock ordering is as follows:
  *   stm::link_mutex
  *     stm::link_lock
  *       src::link_lock
  */
 
 /**
  * stm_source_link_add() - connect an stm_source device to an stm device
  * @src:    stm_source device
  * @stm:    stm device
  *
  * This function establishes a link from stm_source to an stm device so that
  * the former can send out trace data to the latter.
  *
  * Return:  0 on success, -errno otherwise.
  */
 static int stm_source_link_add(struct stm_source_device *src,
                    struct stm_device *stm)
 {
     char *ids[] = { NULL, "default", NULL };
     int err = -ENOMEM;
 
     mutex_lock(&stm->link_mutex);
     spin_lock(&stm->link_lock);
     spin_lock(&src->link_lock);
 
     /* src->link is dereferenced under stm_source_srcu but not the list */
     rcu_assign_pointer(src->link, stm);
     list_add_tail(&src->link_entry, &stm->link_list);
 
     spin_unlock(&src->link_lock);
     spin_unlock(&stm->link_lock);
     mutex_unlock(&stm->link_mutex);
 
     ids[0] = kstrdup(src->data->name, GFP_KERNEL);
     if (!ids[0])
         goto fail_detach;
 
     err = stm_assign_first_policy(stm, &src->output, ids,
                       src->data->nr_chans);
     kfree(ids[0]);
 
     if (err)
         goto fail_detach;
 
     /* this is to notify the STM device that a new link has been made */
     if (stm->data->link)
         err = stm->data->link(stm->data, src->output.master,
                       src->output.channel);
 
     if (err)
         goto fail_free_output;
 
     /* this is to let the source carry out all necessary preparations */
     if (src->data->link)
         src->data->link(src->data);
 
     return 0;
 
 fail_free_output:
     stm_output_free(stm, &src->output);
 
 fail_detach:
     mutex_lock(&stm->link_mutex);
     spin_lock(&stm->link_lock);
     spin_lock(&src->link_lock);
 
     rcu_assign_pointer(src->link, NULL);
     list_del_init(&src->link_entry);
 
     spin_unlock(&src->link_lock);
     spin_unlock(&stm->link_lock);
     mutex_unlock(&stm->link_mutex);
 
     return err;
 }
 
 /**
  * __stm_source_link_drop() - detach stm_source from an stm device
  * @src:    stm_source device
  * @stm:    stm device
  *
  * If @stm is @src::link, disconnect them from one another and put the
  * reference on the @stm device.
  *
  * Caller must hold stm::link_mutex.
  */
 static int __stm_source_link_drop(struct stm_source_device *src,
                   struct stm_device *stm)
 {
     struct stm_device *link;
     int ret = 0;
 
     lockdep_assert_held(&stm->link_mutex);
 
     /* for stm::link_list modification, we hold both mutex and spinlock */
     spin_lock(&stm->link_lock);
     spin_lock(&src->link_lock);
     link = srcu_dereference_check(src->link, &stm_source_srcu, 1);
 
     /*
      * The linked device may have changed since we last looked, because
      * we weren't holding the src::link_lock back then; if this is the
      * case, tell the caller to retry.
      */
     if (link != stm) {
         ret = -EAGAIN;
         goto unlock;
     }
 
     stm_output_free(link, &src->output);
     list_del_init(&src->link_entry);
     pm_runtime_mark_last_busy(&link->dev);
     pm_runtime_put_autosuspend(&link->dev);
     /* matches stm_find_device() from stm_source_link_store() */
     stm_put_device(link);
     rcu_assign_pointer(src->link, NULL);
 
 unlock:
     spin_unlock(&src->link_lock);
     spin_unlock(&stm->link_lock);
 
     /*
      * Call the unlink callbacks for both source and stm, when we know
      * that we have actually performed the unlinking.
      */
     if (!ret) {
         if (src->data->unlink)
             src->data->unlink(src->data);
 
         if (stm->data->unlink)
             stm->data->unlink(stm->data, src->output.master,
                       src->output.channel);
     }
 
     return ret;
 }
 
 /**
  * stm_source_link_drop() - detach stm_source from its stm device
  * @src:    stm_source device
  *
  * Unlinking means disconnecting from source's STM device; after this
  * writes will be unsuccessful until it is linked to a new STM device.
  *
  * This will happen on "stm_source_link" sysfs attribute write to undo
  * the existing link (if any), or on linked STM device's de-registration.
  */
 static void stm_source_link_drop(struct stm_source_device *src)
 {
     struct stm_device *stm;
     int idx, ret;
 
 retry:
     idx = srcu_read_lock(&stm_source_srcu);
     /*
      * The stm device will be valid for the duration of this
      * read section, but the link may change before we grab
      * the src::link_lock in __stm_source_link_drop().
      */
     stm = srcu_dereference(src->link, &stm_source_srcu);
 
     ret = 0;
     if (stm) {
         mutex_lock(&stm->link_mutex);
         ret = __stm_source_link_drop(src, stm);
         mutex_unlock(&stm->link_mutex);
     }
 
     srcu_read_unlock(&stm_source_srcu, idx);
 
     /* if it did change, retry */
     if (ret == -EAGAIN)
         goto retry;
 }
 
 static ssize_t stm_source_link_show(struct device *dev,
                     struct device_attribute *attr,
                     char *buf)
 {
     struct stm_source_device *src = to_stm_source_device(dev);
     struct stm_device *stm;
     int idx, ret;
 
     idx = srcu_read_lock(&stm_source_srcu);
     stm = srcu_dereference(src->link, &stm_source_srcu);
     ret = sprintf(buf, "%s\n",
               stm ? dev_name(&stm->dev) : "<none>");
     srcu_read_unlock(&stm_source_srcu, idx);
 
     return ret;
 }
 
 static ssize_t stm_source_link_store(struct device *dev,
                      struct device_attribute *attr,
                      const char *buf, size_t count)
 {
     struct stm_source_device *src = to_stm_source_device(dev);
     struct stm_device *link;
     int err;
 
     stm_source_link_drop(src);
 
     link = stm_find_device(buf);
     if (!link)
         return -EINVAL;
 
     pm_runtime_get(&link->dev);
 
     err = stm_source_link_add(src, link);
     if (err) {
         pm_runtime_put_autosuspend(&link->dev);
         /* matches the stm_find_device() above */
         stm_put_device(link);
     }
 
     return err ? : count;
 }
 
 static DEVICE_ATTR_RW(stm_source_link);
 
 static struct attribute *stm_source_attrs[] = {
     &dev_attr_stm_source_link.attr,
     NULL,
 };
 
 ATTRIBUTE_GROUPS(stm_source);
 
 static struct class stm_source_class = {
     .name       = "stm_source",
     .dev_groups = stm_source_groups,
 };
 
 static void stm_source_device_release(struct device *dev)
 {
     struct stm_source_device *src = to_stm_source_device(dev);
 
     kfree(src);
 }
 
 /**
  * stm_source_register_device() - register an stm_source device
  * @parent: parent device
  * @data:   device description structure
  *
  * This will create a device of stm_source class that can write
  * data to an stm device once linked.
  *
  * Return:  0 on success, -errno otherwise.
  */
 int stm_source_register_device(struct device *parent,
                    struct stm_source_data *data)
 {
     struct stm_source_device *src;
     int err;
 
     if (!stm_core_up)
         return -EPROBE_DEFER;
 
     src = kzalloc(sizeof(*src), GFP_KERNEL);
     if (!src)
         return -ENOMEM;
 
     device_initialize(&src->dev);
     src->dev.class = &stm_source_class;
     src->dev.parent = parent;
     src->dev.release = stm_source_device_release;
 
     err = kobject_set_name(&src->dev.kobj, "%s", data->name);
     if (err)
         goto err;
 
     pm_runtime_no_callbacks(&src->dev);
     pm_runtime_forbid(&src->dev);
 
     err = device_add(&src->dev);
     if (err)
         goto err;
 
     stm_output_init(&src->output);
     spin_lock_init(&src->link_lock);
     INIT_LIST_HEAD(&src->link_entry);
     src->data = data;
     data->src = src;
 
     return 0;
 
 err:
     put_device(&src->dev);
 
     return err;
 }
 EXPORT_SYMBOL_GPL(stm_source_register_device);
 
 /**
  * stm_source_unregister_device() - unregister an stm_source device
  * @data:   device description that was used to register the device
  *
  * This will remove a previously created stm_source device from the system.
  */
 void stm_source_unregister_device(struct stm_source_data *data)
 {
     struct stm_source_device *src = data->src;
 
     stm_source_link_drop(src);
 
     device_unregister(&src->dev);
 }
 EXPORT_SYMBOL_GPL(stm_source_unregister_device);
 
 int notrace stm_source_write(struct stm_source_data *data,
                  unsigned int chan,
                  const char *buf, size_t count)
 {
     struct stm_source_device *src = data->src;
     struct stm_device *stm;
     int idx;
 
     if (!src->output.nr_chans)
         return -ENODEV;
 
     if (chan >= src->output.nr_chans)
         return -EINVAL;
 
     idx = srcu_read_lock(&stm_source_srcu);
 
     stm = srcu_dereference(src->link, &stm_source_srcu);
     if (stm)
         count = stm_write(stm, &src->output, chan, buf, count);
     else
         count = -ENODEV;
 
     srcu_read_unlock(&stm_source_srcu, idx);
 
     return count;
 }
 EXPORT_SYMBOL_GPL(stm_source_write);
 
 static int __init stm_core_init(void)
 {
     int err;
 
     err = class_register(&stm_class);
     if (err)
         return err;
 
     err = class_register(&stm_source_class);
     if (err)
         goto err_stm;
 
     err = stp_configfs_init();
     if (err)
         goto err_src;
 
     init_srcu_struct(&stm_source_srcu);
     INIT_LIST_HEAD(&stm_pdrv_head);
     mutex_init(&stm_pdrv_mutex);
 
     /*
      * So as to not confuse existing users with a requirement
      * to load yet another module, do it here.
      */
     if (IS_ENABLED(CONFIG_STM_PROTO_BASIC))
         (void)request_module_nowait("stm_p_basic");
     stm_core_up++;
 
     return 0;
 
 err_src:
     class_unregister(&stm_source_class);
 err_stm:
     class_unregister(&stm_class);
 
     return err;
 }
 
 module_init(stm_core_init);
 
 static void __exit stm_core_exit(void)
 {
     cleanup_srcu_struct(&stm_source_srcu);
     class_unregister(&stm_source_class);
     class_unregister(&stm_class);
     stp_configfs_exit();
 }
 
 module_exit(stm_core_exit);
 
 MODULE_LICENSE("GPL v2");
 MODULE_DESCRIPTION("System Trace Module device class");
 MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@linux.intel.com>");

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