[PATCH] mmc: sdhci: Disable SD card clock before changing parameters

[Erick Shepherd]

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@xxxxxx>
Signed-off-by: Brad Mouring <brad.mouring@xxxxxx>
Signed-off-by: Erick Shepherd <erick.shepherd@xxxxxx>
---
 drivers/mmc/host/sdhci.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index f4a7733a8ad2..5f91b44891f9 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -2065,10 +2065,15 @@ 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);
-- 
2.43.0