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From:   Stefan Agner <stefan@agner.ch>
To:     adrian.hunter@intel.com, ulf.hansson@linaro.org
Cc:     fabio.estevam@nxp.com, haibo.chen@nxp.com, aisheng.dong@nxp.com,
        linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Stefan Agner <stefan@agner.ch>
Subject: [PATCH v2 1/2] mmc: sdhci-esdhc-imx: disable clocks before changing frequency
Date:   Thu, 12 Jul 2018 10:06:49 +0200
Message-Id: <20180712080650.13878-1-stefan@agner.ch>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

In the uSDHC case (e.g. i.MX 6) clocks only get disabled if frequency
is set to 0. However, it could be that the stack asks for a frequency
change while clocks are on. In that case the function clears the
divider registers (by clearing ESDHC_CLOCK_MASK) while the clock is
enabled! This causes a short period of time where the clock is
undivided (on a i.MX 6DL a clock of 196MHz has been measured).

For older IP variants the driver disables clock by clearing some bits
in ESDHC_SYSTEM_CONTROL.

Make sure to disable card clock before changing frequency for uSDHC
IP variants too.

Signed-off-by: Stefan Agner <stefan@agner.ch>
---
 drivers/mmc/host/sdhci-esdhc-imx.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
index 85fd5a8b0b6d..acacd8481473 100644
--- a/drivers/mmc/host/sdhci-esdhc-imx.c
+++ b/drivers/mmc/host/sdhci-esdhc-imx.c
@@ -708,14 +708,14 @@ static inline void esdhc_pltfm_set_clock(struct sdhci_host *host,
 	int div = 1;
 	u32 temp, val;
 
+	if (esdhc_is_usdhc(imx_data)) {
+		val = readl(host->ioaddr + ESDHC_VENDOR_SPEC);
+		writel(val & ~ESDHC_VENDOR_SPEC_FRC_SDCLK_ON,
+			host->ioaddr + ESDHC_VENDOR_SPEC);
+	}
+
 	if (clock == 0) {
 		host->mmc->actual_clock = 0;
-
-		if (esdhc_is_usdhc(imx_data)) {
-			val = readl(host->ioaddr + ESDHC_VENDOR_SPEC);
-			writel(val & ~ESDHC_VENDOR_SPEC_FRC_SDCLK_ON,
-					host->ioaddr + ESDHC_VENDOR_SPEC);
-		}
 		return;
 	}
 
-- 
2.18.0