[PATCH v6 17/17] mmc: sdhci-cadence: Support mmc hardware reset

[Brad Larson]

From: Brad Larson <blarson at amd.com>

Add support for mmc hardware reset with a reset-controller
which would need to be enabled in the device tree with
a supporting driver.  The default is disabled for all
existing designs.

Signed-off-by: Brad Larson <blarson at amd.com>
---
 drivers/mmc/host/sdhci-cadence.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/drivers/mmc/host/sdhci-cadence.c b/drivers/mmc/host/sdhci-cadence.c
index c662c63d49fa..35d37b9aba63 100644
--- a/drivers/mmc/host/sdhci-cadence.c
+++ b/drivers/mmc/host/sdhci-cadence.c
@@ -12,6 +12,7 @@
 #include <linux/mmc/mmc.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
+#include <linux/reset.h>
 
 #include "sdhci-pltfm.h"
 
@@ -70,6 +71,7 @@ struct sdhci_cdns_priv {
 	spinlock_t wrlock;	/* write lock */
 	bool enhanced_strobe;
 	void (*priv_writel)(struct sdhci_cdns_priv *priv, u32 val, void __iomem *reg);
+	struct reset_control *rst_hw;
 	unsigned int nr_phy_params;
 	struct sdhci_cdns_phy_param phy_params[];
 };
@@ -458,6 +460,22 @@ static void sdhci_cdns_hs400_enhanced_strobe(struct mmc_host *mmc,
 					 SDHCI_CDNS_HRS06_MODE_MMC_HS400);
 }
 
+static void sdhci_mmc_hw_reset(struct mmc_host *mmc)
+{
+	struct sdhci_host *host = mmc_priv(mmc);
+	struct sdhci_cdns_priv *priv = sdhci_cdns_priv(host);
+
+	dev_info(mmc_dev(host->mmc), "emmc hardware reset\n");
+
+	reset_control_assert(priv->rst_hw);
+	/* For eMMC, minimum is 1us but give it 9us for good measure */
+	udelay(9);
+
+	reset_control_deassert(priv->rst_hw);
+	/* For eMMC, minimum is 200us but give it 300us for good measure */
+	usleep_range(300, 1000);
+}
+
 static int sdhci_cdns_probe(struct platform_device *pdev)
 {
 	struct sdhci_host *host;
@@ -520,6 +538,17 @@ static int sdhci_cdns_probe(struct platform_device *pdev)
 	if (ret)
 		goto free;
 
+	if (host->mmc->caps & MMC_CAP_HW_RESET) {
+		priv->rst_hw = devm_reset_control_get_optional_exclusive(dev, "hw");
+		if (IS_ERR(priv->rst_hw)) {
+			ret = PTR_ERR(priv->rst_hw);
+			if (ret == -ENOENT)
+				priv->rst_hw = NULL;
+		} else {
+			host->mmc_host_ops.card_hw_reset = sdhci_mmc_hw_reset;
+		}
+	}
+
 	ret = sdhci_add_host(host);
 	if (ret)
 		goto free;
-- 
2.17.1