diff options
Diffstat (limited to 'kernel/Documentation/arm/Samsung-S3C24XX/Suspend.txt')
-rw-r--r-- | kernel/Documentation/arm/Samsung-S3C24XX/Suspend.txt | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/kernel/Documentation/arm/Samsung-S3C24XX/Suspend.txt b/kernel/Documentation/arm/Samsung-S3C24XX/Suspend.txt new file mode 100644 index 000000000..1ca63b3e5 --- /dev/null +++ b/kernel/Documentation/arm/Samsung-S3C24XX/Suspend.txt @@ -0,0 +1,137 @@ + S3C24XX Suspend Support + ======================= + + +Introduction +------------ + + The S3C24XX supports a low-power suspend mode, where the SDRAM is kept + in Self-Refresh mode, and all but the essential peripheral blocks are + powered down. For more information on how this works, please look + at the relevant CPU datasheet from Samsung. + + +Requirements +------------ + + 1) A bootloader that can support the necessary resume operation + + 2) Support for at least 1 source for resume + + 3) CONFIG_PM enabled in the kernel + + 4) Any peripherals that are going to be powered down at the same + time require suspend/resume support. + + +Resuming +-------- + + The S3C2410 user manual defines the process of sending the CPU to + sleep and how it resumes. The default behaviour of the Linux code + is to set the GSTATUS3 register to the physical address of the + code to resume Linux operation. + + GSTATUS4 is currently left alone by the sleep code, and is free to + use for any other purposes (for example, the EB2410ITX uses this to + save memory configuration in). + + +Machine Support +--------------- + + The machine specific functions must call the s3c_pm_init() function + to say that its bootloader is capable of resuming. This can be as + simple as adding the following to the machine's definition: + + INITMACHINE(s3c_pm_init) + + A board can do its own setup before calling s3c_pm_init, if it + needs to setup anything else for power management support. + + There is currently no support for over-riding the default method of + saving the resume address, if your board requires it, then contact + the maintainer and discuss what is required. + + Note, the original method of adding an late_initcall() is wrong, + and will end up initialising all compiled machines' pm init! + + The following is an example of code used for testing wakeup from + an falling edge on IRQ_EINT0: + + +static irqreturn_t button_irq(int irq, void *pw) +{ + return IRQ_HANDLED; +} + +statuc void __init machine_init(void) +{ + ... + + request_irq(IRQ_EINT0, button_irq, IRQF_TRIGGER_FALLING, + "button-irq-eint0", NULL); + + enable_irq_wake(IRQ_EINT0); + + s3c_pm_init(); +} + + +Debugging +--------- + + There are several important things to remember when using PM suspend: + + 1) The uart drivers will disable the clocks to the UART blocks when + suspending, which means that use of printascii() or similar direct + access to the UARTs will cause the debug to stop. + + 2) Whilst the pm code itself will attempt to re-enable the UART clocks, + care should be taken that any external clock sources that the UARTs + rely on are still enabled at that point. + + 3) If any debugging is placed in the resume path, then it must have the + relevant clocks and peripherals setup before use (ie, bootloader). + + For example, if you transmit a character from the UART, the baud + rate and uart controls must be setup beforehand. + + +Configuration +------------- + + The S3C2410 specific configuration in `System Type` defines various + aspects of how the S3C2410 suspend and resume support is configured + + `S3C2410 PM Suspend debug` + + This option prints messages to the serial console before and after + the actual suspend, giving detailed information on what is + happening + + + `S3C2410 PM Suspend Memory CRC` + + Allows the entire memory to be checksummed before and after the + suspend to see if there has been any corruption of the contents. + + Note, the time to calculate the CRC is dependent on the CPU speed + and the size of memory. For an 64Mbyte RAM area on an 200MHz + S3C2410, this can take approximately 4 seconds to complete. + + This support requires the CRC32 function to be enabled. + + + `S3C2410 PM Suspend CRC Chunksize (KiB)` + + Defines the size of memory each CRC chunk covers. A smaller value + will mean that the CRC data block will take more memory, but will + identify any faults with better precision + + +Document Author +--------------- + +Ben Dooks, Copyright 2004 Simtec Electronics + |