[PATCH v4 2/8] mmc: sdhci-of-k1: add regulator and pinctrl voltage switching support

[Iker Pedrosa]

Add voltage switching infrastructure for UHS-I modes by integrating both
regulator framework (for supply voltage control) and pinctrl state
switching (for pin drive strength optimization).

- Add regulator supply parsing and voltage switching callback
- Add optional pinctrl state switching between "default" (3.3V) and
  "state_uhs" (1.8V) configurations
- Enable coordinated voltage and pin configuration changes for UHS modes

This provides complete voltage switching support while maintaining
backward compatibility when pinctrl states are not defined.

Tested-by: Anand Moon <linux.amoon at gmail.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 | 72 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/drivers/mmc/host/sdhci-of-k1.c b/drivers/mmc/host/sdhci-of-k1.c
index 0dd06fc19b8574ae1b00f7e5d09b7d4c87d06770..234e258af25996e7bbcd0b70366c7480bf62bee7 100644
--- a/drivers/mmc/host/sdhci-of-k1.c
+++ b/drivers/mmc/host/sdhci-of-k1.c
@@ -16,6 +16,7 @@
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/reset.h>
+#include <linux/pinctrl/consumer.h>
 #include <linux/platform_device.h>
 
 #include "sdhci.h"
@@ -71,6 +72,9 @@
 struct spacemit_sdhci_host {
 	struct clk *clk_core;
 	struct clk *clk_io;
+	struct pinctrl *pinctrl;
+	struct pinctrl_state *pinctrl_default;
+	struct pinctrl_state *pinctrl_uhs;
 };
 
 /* All helper functions will update clr/set while preserve rest bits */
@@ -219,6 +223,46 @@ static void spacemit_sdhci_pre_hs400_to_hs200(struct mmc_host *mmc)
 			       SPACEMIT_SDHC_PHY_CTRL_REG);
 }
 
+static int spacemit_sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
+						      struct mmc_ios *ios)
+{
+	struct sdhci_host *host = mmc_priv(mmc);
+	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
+	struct spacemit_sdhci_host *sdhst = sdhci_pltfm_priv(pltfm_host);
+	struct pinctrl_state *state;
+	int ret;
+
+	ret = sdhci_start_signal_voltage_switch(mmc, ios);
+	if (ret)
+		return ret;
+
+	if (!sdhst->pinctrl)
+		return 0;
+
+	/* Select appropriate pinctrl state based on signal voltage */
+	switch (ios->signal_voltage) {
+	case MMC_SIGNAL_VOLTAGE_330:
+		state = sdhst->pinctrl_default;
+		break;
+	case MMC_SIGNAL_VOLTAGE_180:
+		state = sdhst->pinctrl_uhs;
+		break;
+	default:
+		dev_warn(mmc_dev(mmc), "unsupported voltage %d\n", ios->signal_voltage);
+		return 0;
+	}
+
+	ret = pinctrl_select_state(sdhst->pinctrl, state);
+	if (ret) {
+		dev_warn(mmc_dev(mmc), "failed to select pinctrl state: %d\n", ret);
+		return 0;
+	}
+	dev_dbg(mmc_dev(mmc), "switched to %s pinctrl state\n",
+		ios->signal_voltage == MMC_SIGNAL_VOLTAGE_180 ? "UHS" : "default");
+
+	return 0;
+}
+
 static inline int spacemit_sdhci_get_clocks(struct device *dev,
 					    struct sdhci_pltfm_host *pltfm_host)
 {
@@ -252,6 +296,30 @@ static inline int spacemit_sdhci_get_resets(struct device *dev)
 	return 0;
 }
 
+static inline void spacemit_sdhci_get_pins(struct device *dev,
+					   struct sdhci_pltfm_host *pltfm_host)
+{
+	struct spacemit_sdhci_host *sdhst = sdhci_pltfm_priv(pltfm_host);
+
+	sdhst->pinctrl = devm_pinctrl_get(dev);
+	if (IS_ERR(sdhst->pinctrl)) {
+		sdhst->pinctrl = NULL;
+		dev_dbg(dev, "pinctrl not available, voltage switching will work without it\n");
+		return;
+	}
+
+	sdhst->pinctrl_default = pinctrl_lookup_state(sdhst->pinctrl, "default");
+	if (IS_ERR(sdhst->pinctrl_default))
+		sdhst->pinctrl_default = NULL;
+
+	sdhst->pinctrl_uhs = pinctrl_lookup_state(sdhst->pinctrl, "state_uhs");
+	if (IS_ERR(sdhst->pinctrl_uhs))
+		sdhst->pinctrl_uhs = NULL;
+
+	dev_dbg(dev, "pinctrl setup: default=%p, uhs=%p\n",
+		sdhst->pinctrl_default, sdhst->pinctrl_uhs);
+}
+
 static const struct sdhci_ops spacemit_sdhci_ops = {
 	.get_max_clock		= spacemit_sdhci_clk_get_max_clock,
 	.reset			= spacemit_sdhci_reset,
@@ -324,6 +392,10 @@ static int spacemit_sdhci_probe(struct platform_device *pdev)
 
 	host->mmc->caps |= MMC_CAP_NEED_RSP_BUSY;
 
+	spacemit_sdhci_get_pins(dev, pltfm_host);
+
+	host->mmc_host_ops.start_signal_voltage_switch = spacemit_sdhci_start_signal_voltage_switch;
+
 	ret = spacemit_sdhci_get_clocks(dev, pltfm_host);
 	if (ret)
 		goto err_pltfm;

-- 
2.53.0