mmc: sdhci-sprd: Enable PHY DLL to make clock stable

For the Spreadtrum SD host controller, when we changed the clock to be
more than 52M, we should enable the PHY DLL which is used to track the
clock frequency to make the clock work more stable. Otherwise deviation
may occur of the higher clock.
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci-sprd.c

@@ -22,6 +22,13 @@
 /* SDHCI_ARGUMENT2 register high 16bit */
 #define SDHCI_SPRD_ARG2_STUFF		GENMASK(31, 16)
 
+#define SDHCI_SPRD_REG_32_DLL_CFG	0x200
+#define  SDHCI_SPRD_DLL_ALL_CPST_EN	(BIT(18) | BIT(24) | BIT(25) | BIT(26) | BIT(27))
+#define  SDHCI_SPRD_DLL_EN		BIT(21)
+#define  SDHCI_SPRD_DLL_SEARCH_MODE	BIT(16)
+#define  SDHCI_SPRD_DLL_INIT_COUNT	0xc00
+#define  SDHCI_SPRD_DLL_PHASE_INTERNAL	0x3
+
 #define SDHCI_SPRD_REG_32_DLL_DLY_OFFSET	0x208
 #define  SDHCIBSPRD_IT_WR_DLY_INV		BIT(5)
 #define  SDHCI_SPRD_BIT_CMD_DLY_INV		BIT(13)
@@ -56,6 +63,7 @@
 #define SDHCI_SPRD_CLK_MAX_DIV		1023
 
 #define SDHCI_SPRD_CLK_DEF_RATE		26000000
+#define SDHCI_SPRD_PHY_DLL_CLK		52000000
 
 struct sdhci_sprd_host {
 	u32 version;
@@ -200,9 +208,33 @@ static inline void _sdhci_sprd_set_clock(struct sdhci_host *host,
 	}
 }
 
+static void sdhci_sprd_enable_phy_dll(struct sdhci_host *host)
+{
+	u32 tmp;
+
+	tmp = sdhci_readl(host, SDHCI_SPRD_REG_32_DLL_CFG);
+	tmp &= ~(SDHCI_SPRD_DLL_EN | SDHCI_SPRD_DLL_ALL_CPST_EN);
+	sdhci_writel(host, tmp, SDHCI_SPRD_REG_32_DLL_CFG);
+	/* wait 1ms */
+	usleep_range(1000, 1250);
+
+	tmp = sdhci_readl(host, SDHCI_SPRD_REG_32_DLL_CFG);
+	tmp |= SDHCI_SPRD_DLL_ALL_CPST_EN | SDHCI_SPRD_DLL_SEARCH_MODE |
+		SDHCI_SPRD_DLL_INIT_COUNT | SDHCI_SPRD_DLL_PHASE_INTERNAL;
+	sdhci_writel(host, tmp, SDHCI_SPRD_REG_32_DLL_CFG);
+	/* wait 1ms */
+	usleep_range(1000, 1250);
+
+	tmp = sdhci_readl(host, SDHCI_SPRD_REG_32_DLL_CFG);
+	tmp |= SDHCI_SPRD_DLL_EN;
+	sdhci_writel(host, tmp, SDHCI_SPRD_REG_32_DLL_CFG);
+	/* wait 1ms */
+	usleep_range(1000, 1250);
+}
+
 static void sdhci_sprd_set_clock(struct sdhci_host *host, unsigned int clock)
 {
-	bool en = false;
+	bool en = false, clk_changed = false;
 
 	if (clock == 0) {
 		sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
@@ -214,9 +246,19 @@ static void sdhci_sprd_set_clock(struct sdhci_host *host, unsigned int clock)
 			en = true;
 		sdhci_sprd_set_dll_invert(host, SDHCI_SPRD_BIT_CMD_DLY_INV |
 					  SDHCI_SPRD_BIT_POSRD_DLY_INV, en);
+		clk_changed = true;
 	} else {
 		_sdhci_sprd_set_clock(host, clock);
 	}
+
+	/*
+	 * According to the Spreadtrum SD host specification, when we changed
+	 * the clock to be more than 52M, we should enable the PHY DLL which
+	 * is used to track the clock frequency to make the clock work more
+	 * stable. Otherwise deviation may occur of the higher clock.
+	 */
+	if (clk_changed && clock > SDHCI_SPRD_PHY_DLL_CLK)
+		sdhci_sprd_enable_phy_dll(host);
 }
 
 static unsigned int sdhci_sprd_get_max_clock(struct sdhci_host *host)