From 5f755ba95ae10fd4fa28d64345056ffc18d12c5a Mon Sep 17 00:00:00 2001 From: Erick Shepherd Date: Thu, 24 Jul 2025 13:53:54 -0500 Subject: [PATCH] mmc: sdhci: Disable SD card clock before changing parameters MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Brad Mouring Signed-off-by: Erick Shepherd Acked-by: Adrian Hunter Link: https://lore.kernel.org/r/20250724185354.815888-1-erick.shepherd@ni.com Signed-off-by: Ulf Hansson --- drivers/mmc/host/sdhci-pci-core.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/drivers/mmc/host/sdhci-pci-core.c b/drivers/mmc/host/sdhci-pci-core.c index 826958992dfe2..47a0a738862b5 100644 --- 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, -- 2.47.3