mmc: sdhci_am654: Clear HISPD_ENA in some lower speed modes

According to the AM654x Data Manual[1], the setup timing in lower speed
modes can only be met if the controller uses a falling edge data launch.

To ensure this, the HIGH_SPEED_ENA (HOST_CONTROL[2]) bit should be
cleared in default speed, SD high speed, MMC high speed, SDR12 and SDR25
speed modes.

Use the sdhci writeb callback to implement this condition.

[1] http://www.ti.com/lit/gpn/am6546 Section 5.10.5.16.1
Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/Kconfig

@@ -994,6 +994,7 @@ config MMC_SDHCI_OMAP
 config MMC_SDHCI_AM654
 	tristate "Support for the SDHCI Controller in TI's AM654 SOCs"
 	depends on MMC_SDHCI_PLTFM && OF
+	select MMC_SDHCI_IO_ACCESSORS
 	help
 	  This selects the Secure Digital Host Controller Interface (SDHCI)
 	  support present in TI's AM654 SOCs. The controller supports

drivers/mmc/host/sdhci_am654.c

@@ -158,6 +158,27 @@ static void sdhci_am654_set_power(struct sdhci_host *host, unsigned char mode,
 	sdhci_set_power_noreg(host, mode, vdd);
 }
 
+static void sdhci_am654_write_b(struct sdhci_host *host, u8 val, int reg)
+{
+	unsigned char timing = host->mmc->ios.timing;
+
+	if (reg == SDHCI_HOST_CONTROL) {
+		switch (timing) {
+		/*
+		 * According to the data manual, HISPD bit
+		 * should not be set in these speed modes.
+		 */
+		case MMC_TIMING_SD_HS:
+		case MMC_TIMING_MMC_HS:
+		case MMC_TIMING_UHS_SDR12:
+		case MMC_TIMING_UHS_SDR25:
+			val &= ~SDHCI_CTRL_HISPD;
+		}
+	}
+
+	writeb(val, host->ioaddr + reg);
+}
+
 static struct sdhci_ops sdhci_am654_ops = {
 	.get_max_clock = sdhci_pltfm_clk_get_max_clock,
 	.get_timeout_clock = sdhci_pltfm_clk_get_max_clock,
@@ -165,6 +186,7 @@ static struct sdhci_ops sdhci_am654_ops = {
 	.set_bus_width = sdhci_set_bus_width,
 	.set_power = sdhci_am654_set_power,
 	.set_clock = sdhci_am654_set_clock,
+	.write_b = sdhci_am654_write_b,
 	.reset = sdhci_reset,
 };