mirror of
https://github.com/torvalds/linux.git
synced 2024-12-26 21:02:19 +00:00
50f430e3ad
The (c) alone is not a sufficient copyright statement, nor is it a good replacement for the proper encircled © symbol [1]. Add the word copyright to the apropriate places and remove the (c) symbol. [1] http://www.copyrightservice.co.uk/copyright/p03_copyright_notices section 4 'What does a notice consist of?' Signed-off-by: Ben Dooks <ben@simtec.co.uk> Signed-off-by: Simtec Linux Team <linux@simtec.co.uk> Signed-off-by: Ben Dooks <ben-linux@fluff.org>
138 lines
3.9 KiB
Plaintext
138 lines
3.9 KiB
Plaintext
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 dependant 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
|
|
|