mmc: sdhci-of-at91: Support external regulators

The SDHCI controller in the SAMA5D2 chip requires a valid voltage set
in the power control register, otherwise commands will fail with a
timeout error.

When using the regulator framework to specify the regulator used by the
mmc device, the voltage is not configured, and it is not possible to use
the connected device.

Implement a custom 'set_power' function for this specific hardware, that
configures the voltage in the register in all cases.

Signed-off-by: Romain Izard <romain.izard.pro@gmail.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Cc: stable@vger.kernel.org #4.9+
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

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

@@ -85,11 +85,30 @@ static void sdhci_at91_set_clock(struct sdhci_host *host, unsigned int clock)
 	sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
 }
 
+/*
+ * In this specific implementation of the SDHCI controller, the power register
+ * needs to have a valid voltage set even when the power supply is managed by
+ * an external regulator.
+ */
+static void sdhci_at91_set_power(struct sdhci_host *host, unsigned char mode,
+		     unsigned short vdd)
+{
+	if (!IS_ERR(host->mmc->supply.vmmc)) {
+		struct mmc_host *mmc = host->mmc;
+
+		spin_unlock_irq(&host->lock);
+		mmc_regulator_set_ocr(mmc, mmc->supply.vmmc, vdd);
+		spin_lock_irq(&host->lock);
+	}
+	sdhci_set_power_noreg(host, mode, vdd);
+}
+
 static const struct sdhci_ops sdhci_at91_sama5d2_ops = {
 	.set_clock		= sdhci_at91_set_clock,
 	.set_bus_width		= sdhci_set_bus_width,
 	.reset			= sdhci_reset,
 	.set_uhs_signaling	= sdhci_set_uhs_signaling,
+	.set_power		= sdhci_at91_set_power,
 };
 
 static const struct sdhci_pltfm_data soc_data_sama5d2 = {