mmc: sdhci: enable preset value after uhs initialization

According to the Host Controller spec v3.00, setting Preset Value Enable
in the Host Control2 register lets SDCLK Frequency Select, Clock Generator
Select and Driver Strength Select to be set automatically by the Host
Controller based on the UHS-I mode set. This patch enables this feature.
Since Preset Value Enable makes sense only for UHS-I cards, we enable this
feature after successfull UHS-I initialization. We also reset Preset Value
Enable next time before initialization.

Tested by Zhangfei Gao with a Toshiba uhs card and general hs card,
on mmp2 in SDMA mode.

Signed-off-by: Arindam Nath <arindam.nath@amd.com>
Reviewed-by: Philip Rakity <prakity@marvell.com>
Tested-by: Philip Rakity <prakity@marvell.com>
Acked-by: Zhangfei Gao <zhangfei.gao@marvell.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/sd.c

@@ -925,6 +925,13 @@ static int mmc_sd_init_card(struct mmc_host *host, u32 ocr,
 
 		/* Card is an ultra-high-speed card */
 		mmc_sd_card_set_uhs(card);
+
+		/*
+		 * Since initialization is now complete, enable preset
+		 * value registers for UHS-I cards.
+		 */
+		if (host->ops->enable_preset_value)
+			host->ops->enable_preset_value(host, true);
 	} else {
 		/*
 		 * Attempt to change to high-speed (if supported)
@@ -1095,6 +1102,10 @@ int mmc_attach_sd(struct mmc_host *host)
 	if (err)
 		return err;
 
+	/* Disable preset value enable if already set since last time */
+	if (host->ops->enable_preset_value)
+		host->ops->enable_preset_value(host, false);
+
 	err = mmc_send_app_op_cond(host, 0, &ocr);
 	if (err)
 		return err;

drivers/mmc/host/sdhci.c

@@ -1649,13 +1649,45 @@ static int sdhci_execute_tuning(struct mmc_host *mmc)
 	return err;
 }
 
+static void sdhci_enable_preset_value(struct mmc_host *mmc, bool enable)
+{
+	struct sdhci_host *host;
+	u16 ctrl;
+	unsigned long flags;
+
+	host = mmc_priv(mmc);
+
+	/* Host Controller v3.00 defines preset value registers */
+	if (host->version < SDHCI_SPEC_300)
+		return;
+
+	spin_lock_irqsave(&host->lock, flags);
+
+	ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
+
+	/*
+	 * We only enable or disable Preset Value if they are not already
+	 * enabled or disabled respectively. Otherwise, we bail out.
+	 */
+	if (enable && !(ctrl & SDHCI_CTRL_PRESET_VAL_ENABLE)) {
+		ctrl |= SDHCI_CTRL_PRESET_VAL_ENABLE;
+		sdhci_writew(host, ctrl, SDHCI_HOST_CONTROL2);
+	} else if (!enable && (ctrl & SDHCI_CTRL_PRESET_VAL_ENABLE)) {
+		ctrl &= ~SDHCI_CTRL_PRESET_VAL_ENABLE;
+		sdhci_writew(host, ctrl, SDHCI_HOST_CONTROL2);
+	}
+
+	spin_unlock_irqrestore(&host->lock, flags);
+}
+
 static const struct mmc_host_ops sdhci_ops = {
 	.request	= sdhci_request,
 	.set_ios	= sdhci_set_ios,
 	.get_ro		= sdhci_get_ro,
 	.enable_sdio_irq = sdhci_enable_sdio_irq,
 	.start_signal_voltage_switch	= sdhci_start_signal_voltage_switch,
 	.execute_tuning			= sdhci_execute_tuning,
+	.enable_preset_value		= sdhci_enable_preset_value,
 };
 
 /*****************************************************************************\

include/linux/mmc/host.h

@@ -137,6 +137,7 @@ struct mmc_host_ops {
 
 	int	(*start_signal_voltage_switch)(struct mmc_host *host, struct mmc_ios *ios);
 	int	(*execute_tuning)(struct mmc_host *host);
+	void	(*enable_preset_value)(struct mmc_host *host, bool enable);
 };
 
 struct mmc_card;