mmc: sdhci: Disable SD card clock before changing parameters

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. This change is limited to Intel host controllers to
avoid an issue reported on ARM64 devices.

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/20250724185354.815888-1-erick.shepherd@ni.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

diff --git a/drivers/mmc/host/sdhci-pci-core.c b/drivers/mmc/host/sdhci-pci-core.c
index 826958992dfe265c41e0821c72f95565f81c9c0b..47a0a738862b58f490d7ff1e7ffd037674540e85 100644 (file)
--- a/drivers/mmc/host/sdhci-pci-core.c
+++ b/drivers/mmc/host/sdhci-pci-core.c
@@ -679,8 +679,19 @@ static int intel_start_signal_voltage_switch(struct mmc_host *mmc,
        return 0;
 }
 
+static void sdhci_intel_set_clock(struct sdhci_host *host, unsigned int clock)
+{
+       u16 clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+
+       /* Stop card clock separately to avoid glitches on clock line */
+       if (clk & SDHCI_CLOCK_CARD_EN)
+               sdhci_writew(host, clk & ~SDHCI_CLOCK_CARD_EN, SDHCI_CLOCK_CONTROL);
+
+       sdhci_set_clock(host, clock);
+}
+
 static const struct sdhci_ops sdhci_intel_byt_ops = {
-       .set_clock              = sdhci_set_clock,
+       .set_clock              = sdhci_intel_set_clock,
        .set_power              = sdhci_intel_set_power,
        .enable_dma             = sdhci_pci_enable_dma,
        .set_bus_width          = sdhci_set_bus_width,
@@ -690,7 +701,7 @@ static const struct sdhci_ops sdhci_intel_byt_ops = {
 };
 
 static const struct sdhci_ops sdhci_intel_glk_ops = {
-       .set_clock              = sdhci_set_clock,
+       .set_clock              = sdhci_intel_set_clock,
        .set_power              = sdhci_intel_set_power,
        .enable_dma             = sdhci_pci_enable_dma,
        .set_bus_width          = sdhci_set_bus_width,