gpio: Handle counting of Freescale chipselects

We have a special quirk to handle the Freescale
nonstandard SPI chipselect GPIOs in the gpiolib-of.c
file, but it currently only handles the case where
the GPIOs are actually requested (gpiod_*get()).

We also need to handle that the SPI core attempts
to count the GPIOs before use, and that needs a
similar quirk in the OF part of the library.

Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Reported-by: Christophe Leroy <christophe.leroy@c-s.fr>
Fixes: 0f0581b2 ("spi: fsl: Convert to use CS GPIO descriptors")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>
Link: https://lore.kernel.org/r/20191128083718.39177-2-linus.walleij@linaro.orgSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/gpio/gpiolib-of.c

@@ -23,6 +23,29 @@
 #include "gpiolib.h"
 #include "gpiolib-of.h"
 
+/**
+ * of_gpio_spi_cs_get_count() - special GPIO counting for SPI
+ * Some elder GPIO controllers need special quirks. Currently we handle
+ * the Freescale GPIO controller with bindings that doesn't use the
+ * established "cs-gpios" for chip selects but instead rely on
+ * "gpios" for the chip select lines. If we detect this, we redirect
+ * the counting of "cs-gpios" to count "gpios" transparent to the
+ * driver.
+ */
+int of_gpio_spi_cs_get_count(struct device *dev, const char *con_id)
+{
+	struct device_node *np = dev->of_node;
+
+	if (!IS_ENABLED(CONFIG_SPI_MASTER))
+		return 0;
+	if (!con_id || strcmp(con_id, "cs"))
+		return 0;
+	if (!of_device_is_compatible(np, "fsl,spi") &&
+	    !of_device_is_compatible(np, "aeroflexgaisler,spictrl"))
+		return 0;
+	return of_gpio_named_count(np, "gpios");
+}
+
 /*
  * This is used by external users of of_gpio_count() from <linux/of_gpio.h>
  *
@@ -35,6 +58,10 @@ int of_gpio_get_count(struct device *dev, const char *con_id)
 	char propname[32];
 	unsigned int i;
 
+	ret = of_gpio_spi_cs_get_count(dev, con_id);
+	if (ret > 0)
+		return ret;
+
 	for (i = 0; i < ARRAY_SIZE(gpio_suffixes); i++) {
 		if (con_id)
 			snprintf(propname, sizeof(propname), "%s-%s",