Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 137 insertions, 0 deletions

diff --git a/Documentation/arm/Samsung-S3C24XX/Suspend.txt b/Documentation/arm/Samsung-S3C24XX/Suspend.txt
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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
+