linux-kernel - [PATCH v2 1/2] mmc: sdhci-esdhc-imx: disable clocks before changing frequency

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Message-Id: <20180712080725.14250-1-stefan@agner.ch>
Date:   Thu, 12 Jul 2018 10:07:24 +0200
From:   Stefan Agner <stefan@...er.ch>
To:     adrian.hunter@...el.com, ulf.hansson@...aro.org
Cc:     fabio.estevam@....com, haibo.chen@....com, aisheng.dong@....com,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stefan Agner <stefan@...er.ch>
Subject: [PATCH v2 1/2] mmc: sdhci-esdhc-imx: disable clocks before changing frequency

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@...er.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