[PATCH v4 1/8] mmc: sdhci-of-k1: enable essential clock infrastructure for SD operation

[Iker Pedrosa]

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 at gmail.com>
Acked-by: Adrian Hunter <adrian.hunter at intel.com>
Tested-by: Trevor Gamblin <tgamblin at baylibre.com>
Signed-off-by: Iker Pedrosa <ikerpedrosam at 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