[PATCH v3 4/4] aspeed/watchdog: Add access_cs0 option for alt-boot

From: Ivan Mikhaylov
Date: Tue Aug 27 2019 - 12:55:01 EST

The option for the ast2400/2500 to get access to CS0 at runtime.

Signed-off-by: Ivan Mikhaylov <i.mikhaylov@xxxxxxxxx>
.../ABI/testing/sysfs-class-watchdog | 34 +++++++++++++++++++
1 file changed, 34 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-class-watchdog b/Documentation/ABI/testing/sysfs-class-watchdog
index 6317ade5ad19..675f9b537661 100644
--- a/Documentation/ABI/testing/sysfs-class-watchdog
+++ b/Documentation/ABI/testing/sysfs-class-watchdog
@@ -72,3 +72,37 @@ Description:
It is a read/write file. When read, the currently assigned
pretimeout governor is returned. When written, it sets
the pretimeout governor.
+What: /sys/class/watchdog/watchdog1/access_cs0
+Date: August 2019
+Contact: Ivan Mikhaylov <i.mikhaylov@xxxxxxxxx>,
+ Alexander Amelkin <a.amelkin@xxxxxxxxx>
+ It is a read/write file. This attribute exists only if the
+ system has booted from the alternate flash chip due to
+ expiration of a watchdog timer of AST2400/AST2500 when
+ alternate boot function was enabled with 'aspeed,alt-boot'
+ devicetree option for that watchdog or with an appropriate
+ h/w strapping (for WDT2 only).
+ At alternate flash the 'access_cs0' sysfs node provides:
+ ast2400: a way to get access to the primary SPI flash
+ chip at CS0 after booting from the alternate
+ chip at CS1.
+ ast2500: a way to restore the normal address mapping
+ from (CS0->CS1, CS1->CS0) to (CS0->CS0,
+ CS1->CS1).
+ Clearing the boot code selection and timeout counter also
+ resets to the initial state the chip select line mapping. When
+ the SoC is in normal mapping state (i.e. booted from CS0),
+ clearing those bits does nothing for both versions of the SoC.
+ For alternate boot mode (booted from CS1 due to wdt2
+ expiration) the behavior differs as described above.
+ This option can be used with wdt2 (watchdog1) only.
+ When read, the current status of the boot code selection is
+ shown. When written with any non-zero value, it clears
+ the boot code selection and the timeout counter, which results
+ in chipselect reset for AST2400/AST2500.