linux-kernel - [PATCH v4 4/4] aspeed/watchdog: Add access

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Date:   Wed, 28 Aug 2019 13:24:02 +0300
From:   Ivan Mikhaylov <i.mikhaylov@...ro.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>
CC:     Joel Stanley <joel@....id.au>, Andrew Jeffery <andrew@...id.au>,
        <linux-watchdog@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-aspeed@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>,
        Alexander Amelkin <a.amelkin@...ro.com>,
        <openbmc@...ts.ozlabs.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        <devicetree@...r.kernel.org>,
        Ivan Mikhaylov <i.mikhaylov@...ro.com>
Subject: [PATCH v4 4/4] aspeed/watchdog: Add access_cs0 option for alt-boot

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

Signed-off-by: Ivan Mikhaylov <i.mikhaylov@...ro.com>
---
 .../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@...ro.com>,
+		Alexander Amelkin <a.amelkin@...ro.com>
+Description:
+		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.
-- 
2.20.1