mmc: sdhci-of-at91: add hw_reset callback

Add hardware reset callback that can reset an eMMC.
This is only used in combination with specific DT property cap-mmc-hw-reset.
It uses the MC1R register to enable and disable the reset pin.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>

Author: ehristev

drivers/mmc/host/sdhci-of-at91.c

@@ -25,6 +25,7 @@
 
 #define SDMMC_MC1R	0x204
 #define		SDMMC_MC1R_DDR		BIT(3)
+#define		SDMMC_MC1R_RSTN		BIT(6)
 #define		SDMMC_MC1R_FCD		BIT(7)
 #define SDMMC_CACR	0x230
 #define		SDMMC_CACR_CAPWREN	BIT(0)
@@ -153,12 +154,31 @@ static void sdhci_at91_reset(struct sdhci_host *host, u8 mask)
 	}
 }
 
+static void sdhci_at91_hw_reset(struct sdhci_host *host)
+{
+	u8 mc1r;
+
+	mc1r = readb(host->ioaddr + SDMMC_MC1R);
+
+	mc1r |= SDMMC_MC1R_RSTN;
+	writeb(mc1r, host->ioaddr + SDMMC_MC1R);
+
+	udelay(10);
+
+	mc1r &= ~SDMMC_MC1R_RSTN;
+	writeb(mc1r, host->ioaddr + SDMMC_MC1R);
+
+	/* JEDEC specifies a minimum of 200us for tRSCA (reset to command) */
+	usleep_range(200, 500);
+}
+
 static const struct sdhci_ops sdhci_at91_sama5d2_ops = {
 	.set_clock		= sdhci_at91_set_clock,
 	.set_bus_width		= sdhci_set_bus_width,
 	.reset			= sdhci_at91_reset,
 	.set_uhs_signaling	= sdhci_at91_set_uhs_signaling,
 	.set_power		= sdhci_set_power_and_bus_voltage,
+	.hw_reset		= sdhci_at91_hw_reset,
 };
 
 static const struct sdhci_pltfm_data sdhci_sama5d2_pdata = {