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

[Stefan Agner]

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 <ste...@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