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- S3C24XX Suspend Support
- =======================
- Introduction
- ------------
- The S3C2410 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 S3C2410 datasheets 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 s3c2410_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(s3c2410_pm_init)
- A board can do its own setup before calling s3c2410_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!
- 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.
- 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.
- 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, (c) 2004 Simtec Electronics
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