[PATCH 4/4] mmc: pwrseq_simple: Add support for a reset GPIO pin

[Ulf Hansson <ulf.hansson@linaro.org>]

The need for a reset GPIO has several times been pointed out from
earlier posted patchsets. Especially some WLAN chips which are
attached to an SDIO interface may use a GPIO reset.

In this first version, one reset pin is supported. We may want to
extend the support to cover more pins, but let's leave that as a future
change. The added DT binding for the reset GPIO can easily be extended
to manage several pins.

The reset GPIO is asserted at initialization and prior we start the
power up procedure. It will then be de-asserted right after the power
has been provided for the external chip/card, from the ->power_on()
callback.

Note, the reset GPIO is optional. Thus we don't return an error even if
we can't find a GPIO pin for the consumer.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---
 .../devicetree/bindings/mmc/mmc,pwrseq-simple.txt  |  5 +++
 drivers/mmc/core/pwrseq_simple.c                   | 38 ++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/Documentation/devicetree/bindings/mmc/mmc,pwrseq-simple.txt b/Documentation/devicetree/bindings/mmc/mmc,pwrseq-simple.txt
index e1b7f9c..6fe0cd6 100644
--- a/Documentation/devicetree/bindings/mmc/mmc,pwrseq-simple.txt
+++ b/Documentation/devicetree/bindings/mmc/mmc,pwrseq-simple.txt
@@ -11,8 +11,13 @@ for several SOC designs.
 Required properties:
 - compatible : contains "mmc,pwrseq-simple".
 
+Optional properties:
+- reset-gpios : contains a list of GPIO specifiers, though currently only one
+		specifier is supported.
+
 Example:
 
 	sdhci0_pwrseq {
 		compatible = "mmc,pwrseq-simple";
+		reset-gpios = <&gpio1 12 0>;
 	}
diff --git a/drivers/mmc/core/pwrseq_simple.c b/drivers/mmc/core/pwrseq_simple.c
index 7f87bc1..97112b1 100644
--- a/drivers/mmc/core/pwrseq_simple.c
+++ b/drivers/mmc/core/pwrseq_simple.c
@@ -11,6 +11,7 @@
 #include <linux/slab.h>
 #include <linux/device.h>
 #include <linux/err.h>
+#include <linux/gpio/consumer.h>
 
 #include <linux/mmc/host.h>
 
@@ -18,31 +19,68 @@
 
 struct mmc_pwrseq_simple {
 	struct mmc_pwrseq pwrseq;
+	struct gpio_desc *reset_gpio;
 };
 
+static void mmc_pwrseq_simple_power_up(struct mmc_host *host)
+{
+	struct mmc_pwrseq_simple *pwrseq = container_of(host->pwrseq,
+					struct mmc_pwrseq_simple, pwrseq);
+
+	if (!IS_ERR(pwrseq->reset_gpio))
+		gpiod_set_value_cansleep(pwrseq->reset_gpio, 1);
+}
+
+static void mmc_pwrseq_simple_power_on(struct mmc_host *host)
+{
+	struct mmc_pwrseq_simple *pwrseq = container_of(host->pwrseq,
+					struct mmc_pwrseq_simple, pwrseq);
+
+	if (!IS_ERR(pwrseq->reset_gpio))
+		gpiod_set_value_cansleep(pwrseq->reset_gpio, 0);
+}
+
 static void mmc_pwrseq_simple_free(struct mmc_host *host)
 {
 	struct mmc_pwrseq_simple *pwrseq = container_of(host->pwrseq,
 					struct mmc_pwrseq_simple, pwrseq);
 
+	if (!IS_ERR(pwrseq->reset_gpio))
+		gpiod_put(pwrseq->reset_gpio);
+
 	kfree(&pwrseq);
 	host->pwrseq = NULL;
 }
 
 static struct mmc_pwrseq_ops mmc_pwrseq_simple_ops = {
+	.power_up = mmc_pwrseq_simple_power_up,
+	.power_on = mmc_pwrseq_simple_power_on,
+	.power_off = mmc_pwrseq_simple_power_up,
 	.free = mmc_pwrseq_simple_free,
 };
 
 int mmc_pwrseq_simple_alloc(struct mmc_host *host, struct device *dev)
 {
 	struct mmc_pwrseq_simple *pwrseq;
+	int ret = 0;
 
 	pwrseq = kzalloc(sizeof(struct mmc_pwrseq_simple), GFP_KERNEL);
 	if (!pwrseq)
 		return -ENOMEM;
 
+	pwrseq->reset_gpio = gpiod_get_index(dev, "reset", 0, GPIOD_OUT_HIGH);
+	if (IS_ERR(pwrseq->reset_gpio) &&
+		PTR_ERR(pwrseq->reset_gpio) != -ENOENT &&
+		PTR_ERR(pwrseq->reset_gpio) != -ENOSYS) {
+		ret = PTR_ERR(pwrseq->reset_gpio);
+		goto free;
+	}
+
 	pwrseq->pwrseq.ops = &mmc_pwrseq_simple_ops;
 	host->pwrseq = &pwrseq->pwrseq;
 
 	return 0;
+free:
+	kfree(&pwrseq);
+	return ret;
 }
-- 
1.9.1