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mmc: sdhci: Disable SD card clock before changing parameters

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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>
This commit is contained in:
Erick Shepherd
2025-07-24 13:53:54 -05:00
committed by Ulf Hansson
parent c17b750b3a
commit 5f755ba95a
1 changed files with 13 additions and 2 deletions
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15
drivers/mmc/host/sdhci-pci-core.c
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@@ -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,