0001 =======================
0002 S3C24XX Suspend Support
0003 =======================
0004
0005
0006 Introduction
0007 ------------
0008
0009 The S3C24XX supports a low-power suspend mode, where the SDRAM is kept
0010 in Self-Refresh mode, and all but the essential peripheral blocks are
0011 powered down. For more information on how this works, please look
0012 at the relevant CPU datasheet from Samsung.
0013
0014
0015 Requirements
0016 ------------
0017
0018 1) A bootloader that can support the necessary resume operation
0019
0020 2) Support for at least 1 source for resume
0021
0022 3) CONFIG_PM enabled in the kernel
0023
0024 4) Any peripherals that are going to be powered down at the same
0025 time require suspend/resume support.
0026
0027
0028 Resuming
0029 --------
0030
0031 The S3C2410 user manual defines the process of sending the CPU to
0032 sleep and how it resumes. The default behaviour of the Linux code
0033 is to set the GSTATUS3 register to the physical address of the
0034 code to resume Linux operation.
0035
0036 GSTATUS4 is currently left alone by the sleep code, and is free to
0037 use for any other purposes (for example, the EB2410ITX uses this to
0038 save memory configuration in).
0039
0040
0041 Machine Support
0042 ---------------
0043
0044 The machine specific functions must call the s3c_pm_init() function
0045 to say that its bootloader is capable of resuming. This can be as
0046 simple as adding the following to the machine's definition:
0047
0048 INITMACHINE(s3c_pm_init)
0049
0050 A board can do its own setup before calling s3c_pm_init, if it
0051 needs to setup anything else for power management support.
0052
0053 There is currently no support for over-riding the default method of
0054 saving the resume address, if your board requires it, then contact
0055 the maintainer and discuss what is required.
0056
0057 Note, the original method of adding an late_initcall() is wrong,
0058 and will end up initialising all compiled machines' pm init!
0059
0060 The following is an example of code used for testing wakeup from
0061 an falling edge on IRQ_EINT0::
0062
0063
0064 static irqreturn_t button_irq(int irq, void *pw)
0065 {
0066 return IRQ_HANDLED;
0067 }
0068
0069 statuc void __init machine_init(void)
0070 {
0071 ...
0072
0073 request_irq(IRQ_EINT0, button_irq, IRQF_TRIGGER_FALLING,
0074 "button-irq-eint0", NULL);
0075
0076 enable_irq_wake(IRQ_EINT0);
0077
0078 s3c_pm_init();
0079 }
0080
0081
0082 Debugging
0083 ---------
0084
0085 There are several important things to remember when using PM suspend:
0086
0087 1) The uart drivers will disable the clocks to the UART blocks when
0088 suspending, which means that use of printascii() or similar direct
0089 access to the UARTs will cause the debug to stop.
0090
0091 2) While the pm code itself will attempt to re-enable the UART clocks,
0092 care should be taken that any external clock sources that the UARTs
0093 rely on are still enabled at that point.
0094
0095 3) If any debugging is placed in the resume path, then it must have the
0096 relevant clocks and peripherals setup before use (ie, bootloader).
0097
0098 For example, if you transmit a character from the UART, the baud
0099 rate and uart controls must be setup beforehand.
0100
0101
0102 Configuration
0103 -------------
0104
0105 The S3C2410 specific configuration in `System Type` defines various
0106 aspects of how the S3C2410 suspend and resume support is configured
0107
0108 `S3C2410 PM Suspend debug`
0109
0110 This option prints messages to the serial console before and after
0111 the actual suspend, giving detailed information on what is
0112 happening
0113
0114
0115 `S3C2410 PM Suspend Memory CRC`
0116
0117 Allows the entire memory to be checksummed before and after the
0118 suspend to see if there has been any corruption of the contents.
0119
0120 Note, the time to calculate the CRC is dependent on the CPU speed
0121 and the size of memory. For an 64Mbyte RAM area on an 200MHz
0122 S3C2410, this can take approximately 4 seconds to complete.
0123
0124 This support requires the CRC32 function to be enabled.
0125
0126
0127 `S3C2410 PM Suspend CRC Chunksize (KiB)`
0128
0129 Defines the size of memory each CRC chunk covers. A smaller value
0130 will mean that the CRC data block will take more memory, but will
0131 identify any faults with better precision
0132
0133
0134 Document Author
0135 ---------------
0136
0137 Ben Dooks, Copyright 2004 Simtec Electronics
