mmc: dt: Allow to specify that no write protect signal is present

Allow to specify in the device-tree that no physical write-protect signal
is connected to a particular instance of a MMC controller. Setting the
property will cause the core will assume that the SD card is always
read-write.

The name for the new property is 'disable-wp' and was chosen based on the
property with the same function from the Synopsys designware mobile storage
host controller DT bindings specification.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/mmc.txt

@@ -21,6 +21,11 @@ Optional properties:
   below for the case, when a GPIO is used for the CD line
 - wp-inverted: when present, polarity on the WP line is inverted. See the note
   below for the case, when a GPIO is used for the WP line
+- disable-wp: When set no physical WP line is present. This property should
+  only be specified when the controller has a dedicated write-protect
+  detection logic. If a GPIO is always used for the write-protect detection
+  logic it is sufficient to not specify wp-gpios property in the absence of a WP
+  line.
 - max-frequency: maximum operating clock frequency
 - no-1-8-v: when present, denotes that 1.8v card voltage is not supported on
   this system, even if the controller claims it is.

drivers/mmc/core/host.c

@@ -484,6 +484,9 @@ int mmc_of_parse(struct mmc_host *host)
 	else if (ret != -ENOENT)
 		return ret;
 
+	if (of_property_read_bool(np, "disable-wp"))
+		host->caps2 |= MMC_CAP2_NO_WRITE_PROTECT;
+
 	/* See the comment on CD inversion above */
 	if (ro_cap_invert ^ ro_gpio_invert)
 		host->caps2 |= MMC_CAP2_RO_ACTIVE_HIGH;