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