scsi: ufs-qcom: Implement device_reset vops

The UFS_RESET pin on Qualcomm SoCs are controlled by TLMM and exposed
through the GPIO framework. Acquire the device-reset GPIO and use this to
implement the device_reset vops, to allow resetting the attached memory.

Based on downstream support implemented by Subhash Jadavani
<subhashj@codeaurora.org>.

Link: https://lore.kernel.org/r/20190828191756.24312-3-bjorn.andersson@linaro.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Avri Altman <Avri.Altman@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt

@@ -54,6 +54,8 @@ Optional properties:
 			  PHY reset from the UFS controller.
 - resets            : reset node register
 - reset-names       : describe reset node register, the "rst" corresponds to reset the whole UFS IP.
+- reset-gpios       : A phandle and gpio specifier denoting the GPIO connected
+		      to the RESET pin of the UFS memory device.
 
 Note: If above properties are not defined it can be assumed that the supply
 regulators or clocks are always on.

drivers/scsi/ufs/ufs-qcom.c

@@ -8,6 +8,7 @@
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/phy/phy.h>
+#include <linux/gpio/consumer.h>
 #include <linux/reset-controller.h>
 
 #include "ufshcd.h"
@@ -1137,6 +1138,15 @@ static int ufs_qcom_init(struct ufs_hba *hba)
 		}
 	}
 
+	host->device_reset = devm_gpiod_get_optional(dev, "reset",
+						     GPIOD_OUT_HIGH);
+	if (IS_ERR(host->device_reset)) {
+		err = PTR_ERR(host->device_reset);
+		if (err != -EPROBE_DEFER)
+			dev_err(dev, "failed to acquire reset gpio: %d\n", err);
+		goto out_variant_clear;
+	}
+
 	err = ufs_qcom_bus_register(host);
 	if (err)
 		goto out_variant_clear;
@@ -1542,6 +1552,31 @@ static void ufs_qcom_dump_dbg_regs(struct ufs_hba *hba)
 	usleep_range(1000, 1100);
 }
 
+/**
+ * ufs_qcom_device_reset() - toggle the (optional) device reset line
+ * @hba: per-adapter instance
+ *
+ * Toggles the (optional) reset line to reset the attached device.
+ */
+static void ufs_qcom_device_reset(struct ufs_hba *hba)
+{
+	struct ufs_qcom_host *host = ufshcd_get_variant(hba);
+
+	/* reset gpio is optional */
+	if (!host->device_reset)
+		return;
+
+	/*
+	 * The UFS device shall detect reset pulses of 1us, sleep for 10us to
+	 * be on the safe side.
+	 */
+	gpiod_set_value_cansleep(host->device_reset, 1);
+	usleep_range(10, 15);
+
+	gpiod_set_value_cansleep(host->device_reset, 0);
+	usleep_range(10, 15);
+}
+
 /**
  * struct ufs_hba_qcom_vops - UFS QCOM specific variant operations
  *
@@ -1562,6 +1597,7 @@ static const struct ufs_hba_variant_ops ufs_hba_qcom_vops = {
 	.suspend		= ufs_qcom_suspend,
 	.resume			= ufs_qcom_resume,
 	.dbg_register_dump	= ufs_qcom_dump_dbg_regs,
+	.device_reset		= ufs_qcom_device_reset,
 };
 
 /**

drivers/scsi/ufs/ufs-qcom.h

@@ -195,6 +195,8 @@ struct ufs_qcom_testbus {
 	u8 select_minor;
 };
 
+struct gpio_desc;
+
 struct ufs_qcom_host {
 	/*
 	 * Set this capability if host controller supports the QUniPro mode
@@ -232,6 +234,8 @@ struct ufs_qcom_host {
 	struct ufs_qcom_testbus testbus;
 
 	struct reset_controller_dev rcdev;
+
+	struct gpio_desc *device_reset;
 };
 
 static inline u32