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137 lines
3.9 KiB
137 lines
3.9 KiB
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S3C24XX Suspend Support |
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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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