cs5535-gpio: apply CS5536 errata workaround for GPIOs

The AMD Geode CS5536 Companion Device Silicon Revision B1 Specification
Update mentions the follow as issue #36:

 "Atomic write transactions to the atomic GPIO High Bank Feature Bit
  registers should only affect the bits selected [...]"

 "after Suspend, an atomic write transaction [...] will clear all
  non-selected bits of the accessed register."

In other words, writing to the high bank for a single GPIO bit will
clear every other GPIO bit (but only sometimes after a suspend).

The workaround described is obvious and simple; do a read-modify-write.
This patch does that, and documents why we're doing it.
Signed-off-by: Andres Salomon <dilinger@queued.net>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/gpio/cs5535-gpio.c

@@ -56,6 +56,18 @@ static struct cs5535_gpio_chip {
  * registers, see include/linux/cs5535.h.
  */
 
+static void errata_outl(u32 val, unsigned long addr)
+{
+	/*
+	 * According to the CS5536 errata (#36), after suspend
+	 * a write to the high bank GPIO register will clear all
+	 * non-selected bits; the recommended workaround is a
+	 * read-modify-write operation.
+	 */
+	val |= inl(addr);
+	outl(val, addr);
+}
+
 static void __cs5535_gpio_set(struct cs5535_gpio_chip *chip, unsigned offset,
 		unsigned int reg)
 {
@@ -64,7 +76,7 @@ static void __cs5535_gpio_set(struct cs5535_gpio_chip *chip, unsigned offset,
 		outl(1 << offset, chip->base + reg);
 	else
 		/* high bank register */
-		outl(1 << (offset - 16), chip->base + 0x80 + reg);
+		errata_outl(1 << (offset - 16), chip->base + 0x80 + reg);
 }
 
 void cs5535_gpio_set(unsigned offset, unsigned int reg)
@@ -86,7 +98,7 @@ static void __cs5535_gpio_clear(struct cs5535_gpio_chip *chip, unsigned offset,
 		outl(1 << (offset + 16), chip->base + reg);
 	else
 		/* high bank register */
-		outl(1 << offset, chip->base + 0x80 + reg);
+		errata_outl(1 << offset, chip->base + 0x80 + reg);
 }
 
 void cs5535_gpio_clear(unsigned offset, unsigned int reg)