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+ 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
+