mmc: sdhci: Disable SD card clock before changing parameters

[ Upstream commit fb3bbc46c94f261b6156ee863c1b06c84cf157dc ]

Per the SD Host Controller Simplified Specification v4.20 §3.2.3, change
the SD card clock parameters only after first disabling the external card
clock. Doing this fixes a spurious clock pulse on Baytrail and Apollo Lake
SD controllers which otherwise breaks voltage switching with a specific
Swissbit SD card.

Signed-off-by: Kyle Roeschley <kyle.roeschley@ni.com>
Signed-off-by: Brad Mouring <brad.mouring@ni.com>
Signed-off-by: Erick Shepherd <erick.shepherd@ni.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20250211214645.469279-1-erick.shepherd@ni.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 9796a3cb3ca62c58750791c8e945a7bf2885b15d..f32429ff905ff66ecca6cc35d277aa19b55b7aa1 100644 (file)
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -2035,10 +2035,15 @@ void sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
 
        host->mmc->actual_clock = 0;
 
-       sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
+       clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+       if (clk & SDHCI_CLOCK_CARD_EN)
+               sdhci_writew(host, clk & ~SDHCI_CLOCK_CARD_EN,
+                       SDHCI_CLOCK_CONTROL);
 
-       if (clock == 0)
+       if (clock == 0) {
+               sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
                return;
+       }
 
        clk = sdhci_calc_clk(host, clock, &host->mmc->actual_clock);
        sdhci_enable_clk(host, clk);