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