[PATCH v5 2/9] mmc: sdhci-of-k1: enable essential clock infrastructure for SD operation

Iker Pedrosa
2026-03-30T08:38:27Z

Ensure SD card pins receive clock signals by enabling pad clock
generation and overriding automatic clock gating. Required for all SD
operation modes.

The SDHC_GEN_PAD_CLK_ON setting in LEGACY_CTRL_REG is safe for both SD
and eMMC operation as both protocols use the same physical MMC interface
pins and require proper clock signal generation at the hardware level
for signal integrity and timing.

Additional SD-specific clock overrides (SDHC_OVRRD_CLK_OEN and
SDHC_FORCE_CLK_ON) are conditionally applied only for SD-only
controllers to handle removable card scenarios.

Tested-by: Anand Moon <linux.amoon@gmail.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Trevor Gamblin <tgamblin@baylibre.com>
Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
---
drivers/mmc/host/sdhci-of-k1.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/drivers/mmc/host/sdhci-of-k1.c b/drivers/mmc/host/sdhci-of-k1.c
index 455656f9842df90c7a94a290aeec22157b378fc1..0dd06fc19b8574ae1b00f7e5d09b7d4c87d06770 100644
--- a/drivers/mmc/host/sdhci-of-k1.c
+++ b/drivers/mmc/host/sdhci-of-k1.c
@@ -21,6 +21,13 @@
#include "sdhci.h"
#include "sdhci-pltfm.h"

+#define SPACEMIT_SDHC_OP_EXT_REG 0x108
+#define SDHC_OVRRD_CLK_OEN BIT(11)
+#define SDHC_FORCE_CLK_ON BIT(12)
+
+#define SPACEMIT_SDHC_LEGACY_CTRL_REG 0x10C
+#define SDHC_GEN_PAD_CLK_ON BIT(6)
+
#define SPACEMIT_SDHC_MMC_CTRL_REG 0x114
#define SDHC_MISC_INT_EN BIT(1)
#define SDHC_MISC_INT BIT(2)
@@ -101,6 +108,12 @@ static void spacemit_sdhci_reset(struct sdhci_host *host, u8 mask)

if (!(host->mmc->caps2 & MMC_CAP2_NO_MMC))
spacemit_sdhci_setbits(host, SDHC_MMC_CARD_MODE, SPACEMIT_SDHC_MMC_CTRL_REG);
+
+ spacemit_sdhci_setbits(host, SDHC_GEN_PAD_CLK_ON, SPACEMIT_SDHC_LEGACY_CTRL_REG);
+
+ if (host->mmc->caps2 & MMC_CAP2_NO_MMC)
+ spacemit_sdhci_setbits(host, SDHC_OVRRD_CLK_OEN | SDHC_FORCE_CLK_ON,
+ SPACEMIT_SDHC_OP_EXT_REG);
}

static void spacemit_sdhci_set_uhs_signaling(struct sdhci_host *host, unsigned int timing)

--
2.53.0