LXR linux/Documentation/arm/samsung-s3c24xx/suspend.rst

   1=======================
   2S3C24XX Suspend Support
   3=======================
   4
   5
   6Introduction
   7------------
   8
   9  The S3C24XX supports a low-power suspend mode, where the SDRAM is kept
  10  in Self-Refresh mode, and all but the essential peripheral blocks are
  11  powered down. For more information on how this works, please look
  12  at the relevant CPU datasheet from Samsung.
  13
  14
  15Requirements
  16------------
  17
  18  1) A bootloader that can support the necessary resume operation
  19
  20  2) Support for at least 1 source for resume
  21
  22  3) CONFIG_PM enabled in the kernel
  23
  24  4) Any peripherals that are going to be powered down at the same
  25     time require suspend/resume support.
  26
  27
  28Resuming
  29--------
  30
  31  The S3C2410 user manual defines the process of sending the CPU to
  32  sleep and how it resumes. The default behaviour of the Linux code
  33  is to set the GSTATUS3 register to the physical address of the
  34  code to resume Linux operation.
  35
  36  GSTATUS4 is currently left alone by the sleep code, and is free to
  37  use for any other purposes (for example, the EB2410ITX uses this to
  38  save memory configuration in).
  39
  40
  41Machine Support
  42---------------
  43
  44  The machine specific functions must call the s3c_pm_init() function
  45  to say that its bootloader is capable of resuming. This can be as
  46  simple as adding the following to the machine's definition:
  47
  48  INITMACHINE(s3c_pm_init)
  49
  50  A board can do its own setup before calling s3c_pm_init, if it
  51  needs to setup anything else for power management support.
  52
  53  There is currently no support for over-riding the default method of
  54  saving the resume address, if your board requires it, then contact
  55  the maintainer and discuss what is required.
  56
  57  Note, the original method of adding an late_initcall() is wrong,
  58  and will end up initialising all compiled machines' pm init!
  59
  60  The following is an example of code used for testing wakeup from
  61  an falling edge on IRQ_EINT0::
  62
  63
  64    static irqreturn_t button_irq(int irq, void *pw)
  65    {
  66        return IRQ_HANDLED;
  67    }
  68
  69    statuc void __init machine_init(void)
  70    {
  71        ...
  72
  73        request_irq(IRQ_EINT0, button_irq, IRQF_TRIGGER_FALLING,
  74                   "button-irq-eint0", NULL);
  75
  76        enable_irq_wake(IRQ_EINT0);
  77
  78        s3c_pm_init();
  79    }
  80
  81
  82Debugging
  83---------
  84
  85  There are several important things to remember when using PM suspend:
  86
  87  1) The uart drivers will disable the clocks to the UART blocks when
  88     suspending, which means that use of printascii() or similar direct
  89     access to the UARTs will cause the debug to stop.
  90
  91  2) While the pm code itself will attempt to re-enable the UART clocks,
  92     care should be taken that any external clock sources that the UARTs
  93     rely on are still enabled at that point.
  94
  95  3) If any debugging is placed in the resume path, then it must have the
  96     relevant clocks and peripherals setup before use (ie, bootloader).
  97
  98     For example, if you transmit a character from the UART, the baud
  99     rate and uart controls must be setup beforehand.
 100
 101
 102Configuration
 103-------------
 104
 105  The S3C2410 specific configuration in `System Type` defines various
 106  aspects of how the S3C2410 suspend and resume support is configured
 107
 108  `S3C2410 PM Suspend debug`
 109
 110    This option prints messages to the serial console before and after
 111    the actual suspend, giving detailed information on what is
 112    happening
 113
 114
 115  `S3C2410 PM Suspend Memory CRC`
 116
 117    Allows the entire memory to be checksummed before and after the
 118    suspend to see if there has been any corruption of the contents.
 119
 120    Note, the time to calculate the CRC is dependent on the CPU speed
 121    and the size of memory. For an 64Mbyte RAM area on an 200MHz
 122    S3C2410, this can take approximately 4 seconds to complete.
 123
 124    This support requires the CRC32 function to be enabled.
 125
 126
 127  `S3C2410 PM Suspend CRC Chunksize (KiB)`
 128
 129    Defines the size of memory each CRC chunk covers. A smaller value
 130    will mean that the CRC data block will take more memory, but will
 131    identify any faults with better precision
 132
 133
 134Document Author
 135---------------
 136
 137Ben Dooks, Copyright 2004 Simtec Electronics
 138