gpu/drm/drm_aperture.c

0001 // SPDX-License-Identifier: MIT
0002
0003 #include <linux/aperture.h>
0004 #include <linux/platform_device.h>
0005
0006 #include <drm/drm_aperture.h>
0007 #include <drm/drm_drv.h>
0008 #include <drm/drm_print.h>
0009
0010 /**
0011  * DOC: overview
0012  *
0013  * A graphics device might be supported by different drivers, but only one
0014  * driver can be active at any given time. Many systems load a generic
0015  * graphics drivers, such as EFI-GOP or VESA, early during the boot process.
0016  * During later boot stages, they replace the generic driver with a dedicated,
0017  * hardware-specific driver. To take over the device the dedicated driver
0018  * first has to remove the generic driver. DRM aperture functions manage
0019  * ownership of DRM framebuffer memory and hand-over between drivers.
0020  *
0021  * DRM drivers should call drm_aperture_remove_conflicting_framebuffers()
0022  * at the top of their probe function. The function removes any generic
0023  * driver that is currently associated with the given framebuffer memory.
0024  * If the framebuffer is located at PCI BAR 0, the rsp code looks as in the
0025  * example given below.
0026  *
0027  * .. code-block:: c
0028  *
0029  *  static const struct drm_driver example_driver = {
0030  *      ...
0031  *  };
0032  *
0033  *  static int remove_conflicting_framebuffers(struct pci_dev *pdev)
0034  *  {
0035  *      bool primary = false;
0036  *      resource_size_t base, size;
0037  *      int ret;
0038  *
0039  *      base = pci_resource_start(pdev, 0);
0040  *      size = pci_resource_len(pdev, 0);
0041  *  #ifdef CONFIG_X86
0042  *      primary = pdev->resource[PCI_ROM_RESOURCE].flags & IORESOURCE_ROM_SHADOW;
0043  *  #endif
0044  *
0045  *      return drm_aperture_remove_conflicting_framebuffers(base, size, primary,
0046  *                                                          &example_driver);
0047  *  }
0048  *
0049  *  static int probe(struct pci_dev *pdev)
0050  *  {
0051  *      int ret;
0052  *
0053  *      // Remove any generic drivers...
0054  *      ret = remove_conflicting_framebuffers(pdev);
0055  *      if (ret)
0056  *          return ret;
0057  *
0058  *      // ... and initialize the hardware.
0059  *      ...
0060  *
0061  *      drm_dev_register();
0062  *
0063  *      return 0;
0064  *  }
0065  *
0066  * PCI device drivers should call
0067  * drm_aperture_remove_conflicting_pci_framebuffers() and let it detect the
0068  * framebuffer apertures automatically. Device drivers without knowledge of
0069  * the framebuffer's location shall call drm_aperture_remove_framebuffers(),
0070  * which removes all drivers for known framebuffer.
0071  *
0072  * Drivers that are susceptible to being removed by other drivers, such as
0073  * generic EFI or VESA drivers, have to register themselves as owners of their
0074  * given framebuffer memory. Ownership of the framebuffer memory is achieved
0075  * by calling devm_aperture_acquire_from_firmware(). On success, the driver
0076  * is the owner of the framebuffer range. The function fails if the
0077  * framebuffer is already by another driver. See below for an example.
0078  *
0079  * .. code-block:: c
0080  *
0081  *  static int acquire_framebuffers(struct drm_device *dev, struct platform_device *pdev)
0082  *  {
0083  *      resource_size_t base, size;
0084  *
0085  *      mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
0086  *      if (!mem)
0087  *          return -EINVAL;
0088  *      base = mem->start;
0089  *      size = resource_size(mem);
0090  *
0091  *      return devm_acquire_aperture_from_firmware(dev, base, size);
0092  *  }
0093  *
0094  *  static int probe(struct platform_device *pdev)
0095  *  {
0096  *      struct drm_device *dev;
0097  *      int ret;
0098  *
0099  *      // ... Initialize the device...
0100  *      dev = devm_drm_dev_alloc();
0101  *      ...
0102  *
0103  *      // ... and acquire ownership of the framebuffer.
0104  *      ret = acquire_framebuffers(dev, pdev);
0105  *      if (ret)
0106  *          return ret;
0107  *
0108  *      drm_dev_register(dev, 0);
0109  *
0110  *      return 0;
0111  *  }
0112  *
0113  * The generic driver is now subject to forced removal by other drivers. This
0114  * only works for platform drivers that support hot unplug.
0115  * When a driver calls drm_aperture_remove_conflicting_framebuffers() et al
0116  * for the registered framebuffer range, the aperture helpers call
0117  * platform_device_unregister() and the generic driver unloads itself. It
0118  * may not access the device's registers, framebuffer memory, ROM, etc
0119  * afterwards.
0120  */
0121
0122 /**
0123  * devm_aperture_acquire_from_firmware - Acquires ownership of a firmware framebuffer
0124  *                                       on behalf of a DRM driver.
0125  * @dev:    the DRM device to own the framebuffer memory
0126  * @base:   the framebuffer's byte offset in physical memory
0127  * @size:   the framebuffer size in bytes
0128  *
0129  * Installs the given device as the new owner of the framebuffer. The function
0130  * expects the framebuffer to be provided by a platform device that has been
0131  * set up by firmware. Firmware can be any generic interface, such as EFI,
0132  * VESA, VGA, etc. If the native hardware driver takes over ownership of the
0133  * framebuffer range, the firmware state gets lost. Aperture helpers will then
0134  * unregister the platform device automatically. Acquired apertures are
0135  * released automatically if the underlying device goes away.
0136  *
0137  * The function fails if the framebuffer range, or parts of it, is currently
0138  * owned by another driver. To evict current owners, callers should use
0139  * drm_aperture_remove_conflicting_framebuffers() et al. before calling this
0140  * function. The function also fails if the given device is not a platform
0141  * device.
0142  *
0143  * Returns:
0144  * 0 on success, or a negative errno value otherwise.
0145  */
0146 int devm_aperture_acquire_from_firmware(struct drm_device *dev, resource_size_t base,
0147                     resource_size_t size)
0148 {
0149     struct platform_device *pdev;
0150
0151     if (drm_WARN_ON(dev, !dev_is_platform(dev->dev)))
0152         return -EINVAL;
0153
0154     pdev = to_platform_device(dev->dev);
0155
0156     return devm_aperture_acquire_for_platform_device(pdev, base, size);
0157 }
0158 EXPORT_SYMBOL(devm_aperture_acquire_from_firmware);
0159
0160 /**
0161  * drm_aperture_remove_conflicting_framebuffers - remove existing framebuffers in the given range
0162  * @base: the aperture's base address in physical memory
0163  * @size: aperture size in bytes
0164  * @primary: also kick vga16fb if present
0165  * @req_driver: requesting DRM driver
0166  *
0167  * This function removes graphics device drivers which use memory range described by
0168  * @base and @size.
0169  *
0170  * Returns:
0171  * 0 on success, or a negative errno code otherwise
0172  */
0173 int drm_aperture_remove_conflicting_framebuffers(resource_size_t base, resource_size_t size,
0174                          bool primary, const struct drm_driver *req_driver)
0175 {
0176     return aperture_remove_conflicting_devices(base, size, primary, req_driver->name);
0177 }
0178 EXPORT_SYMBOL(drm_aperture_remove_conflicting_framebuffers);
0179
0180 /**
0181  * drm_aperture_remove_conflicting_pci_framebuffers - remove existing framebuffers for PCI devices
0182  * @pdev: PCI device
0183  * @req_driver: requesting DRM driver
0184  *
0185  * This function removes graphics device drivers using memory range configured
0186  * for any of @pdev's memory bars. The function assumes that PCI device with
0187  * shadowed ROM drives a primary display and so kicks out vga16fb.
0188  *
0189  * Returns:
0190  * 0 on success, or a negative errno code otherwise
0191  */
0192 int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
0193                              const struct drm_driver *req_driver)
0194 {
0195     return aperture_remove_conflicting_pci_devices(pdev, req_driver->name);
0196 }
0197 EXPORT_SYMBOL(drm_aperture_remove_conflicting_pci_framebuffers);