mmc: sdhci-of-dwcmshc: Disable clock before DLL configuration

According to the ASIC design recommendations, the clock must be
disabled before operating the DLL to prevent glitches that could
affect the internal digital logic. In extreme cases, failing to
do so may cause the controller to malfunction completely.

Adds a step to disable the clock before DLL configuration and
re-enables it at the end.

Fixes: 08f3dff ("mmc: sdhci-of-dwcmshc: add rockchip platform support")
Cc: stable@vger.kernel.org
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: shawn1221

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

@@ -783,12 +783,15 @@ static void dwcmshc_rk3568_set_clock(struct sdhci_host *host, unsigned int clock
 	extra |= BIT(4);
 	sdhci_writel(host, extra, reg);
 
+	/* Disable clock while config DLL */
+	sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
+
 	if (clock <= 52000000) {
 		if (host->mmc->ios.timing == MMC_TIMING_MMC_HS200 ||
 		    host->mmc->ios.timing == MMC_TIMING_MMC_HS400) {
 			dev_err(mmc_dev(host->mmc),
 				"Can't reduce the clock below 52MHz in HS200/HS400 mode");
-			return;
+			goto enable_clk;
 		}
 
 		/*
@@ -808,7 +811,7 @@ static void dwcmshc_rk3568_set_clock(struct sdhci_host *host, unsigned int clock
 			DLL_STRBIN_DELAY_NUM_SEL |
 			DLL_STRBIN_DELAY_NUM_DEFAULT << DLL_STRBIN_DELAY_NUM_OFFSET;
 		sdhci_writel(host, extra, DWCMSHC_EMMC_DLL_STRBIN);
-		return;
+		goto enable_clk;
 	}
 
 	/* Reset DLL */
@@ -835,7 +838,7 @@ static void dwcmshc_rk3568_set_clock(struct sdhci_host *host, unsigned int clock
 				 500 * USEC_PER_MSEC);
 	if (err) {
 		dev_err(mmc_dev(host->mmc), "DLL lock timeout!\n");
-		return;
+		goto enable_clk;
 	}
 
 	extra = 0x1 << 16 | /* tune clock stop en */
@@ -868,6 +871,16 @@ static void dwcmshc_rk3568_set_clock(struct sdhci_host *host, unsigned int clock
 		DLL_STRBIN_TAPNUM_DEFAULT |
 		DLL_STRBIN_TAPNUM_FROM_SW;
 	sdhci_writel(host, extra, DWCMSHC_EMMC_DLL_STRBIN);
+
+enable_clk:
+	/*
+	 * The sdclk frequency select bits in SDHCI_CLOCK_CONTROL are not functional
+	 * on Rockchip's SDHCI implementation. Instead, the clock frequency is fully
+	 * controlled via external clk provider by calling clk_set_rate(). Consequently,
+	 * passing 0 to sdhci_enable_clk() only re-enables the already-configured clock,
+	 * which matches the hardware's actual behavior.
+	 */
+	sdhci_enable_clk(host, 0);
 }
 
 static void rk35xx_sdhci_reset(struct sdhci_host *host, u8 mask)