[PATCH] gpio/spi: Fix spi-gpio regression on active high CS

[Linus Walleij <linus.walleij@linaro.org>]

I ran into an intriguing bug caused by
commit ""spi: gpio: Don't request CS GPIO in DT use-case"
affecting all SPI GPIO devices with an active high
chip select line.

The commit switches the CS gpio handling over to the GPIO
core, which will parse and handle "cs-gpios" from the OF
node without even calling down to the driver to get the
job done.

However the GPIO core handles the standard bindings in
Documentation/devicetree/bindings/spi/spi-controller.yaml
that specifies that active high CS needs to be specified
using "spi-cs-high" in the DT node.

The code in drivers/spi/spi-gpio.c never respected this
and never tried to inspect subnodes to see if they contained
"spi-cs-high" like the gpiolib OF quirks does. Instead the
only way to get an active high CS was to tag it in the
device tree using the flags cell such as
cs-gpios = <&gpio 4 GPIO_ACTIVE_HIGH>;

This alters the quirks to not inspect the subnodes of SPI
masters on "spi-gpio" for the standard attribute "spi-cs-high",
making old device trees work as expected.

This semantic is a bit ambigous, but just allowing the
flags on the GPIO descriptor to modify polarity is what
the kernel at large mostly uses so let's encourage that.

Fixes: 249e2632dcd0 ("spi: gpio: Don't request CS GPIO in DT use-case")
Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: linux-gpio@vger.kernel.org
Cc: linux-spi@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
Mark: I will apply this to the GPIO tree, so I think it is
safe for you to drop my revert of Andrey's patch once this
hits mainline. I will try to expediate it, I feel a bit
responsible.
---
 drivers/gpio/gpiolib-of.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
index aec7bd86ae7e..9c9b965d7d6d 100644
--- a/drivers/gpio/gpiolib-of.c
+++ b/drivers/gpio/gpiolib-of.c
@@ -118,8 +118,15 @@ static void of_gpio_flags_quirks(struct device_node *np,
 	 * Legacy handling of SPI active high chip select. If we have a
 	 * property named "cs-gpios" we need to inspect the child node
 	 * to determine if the flags should have inverted semantics.
+	 *
+	 * This does not apply to an SPI device named "spi-gpio", because
+	 * these have traditionally obtained their own GPIOs by parsing
+	 * the device tree directly and did not respect any "spi-cs-high"
+	 * property on the SPI bus children.
 	 */
-	if (IS_ENABLED(CONFIG_SPI_MASTER) && !strcmp(propname, "cs-gpios") &&
+	if (IS_ENABLED(CONFIG_SPI_MASTER) &&
+	    !strcmp(propname, "cs-gpios") &&
+	    !of_device_is_compatible(np, "spi-gpio") &&
 	    of_property_read_bool(np, "cs-gpios")) {
 		struct device_node *child;
 		u32 cs;
-- 
2.21.0