[PATCH v2 2/7] mmc: sdhci-of-k1: add regulator and pinctrl voltage switching support

[Iker Pedrosa <ikerpedrosam@gmail.com>]

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.

Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
---
 drivers/mmc/host/sdhci-of-k1.c | 59 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/drivers/mmc/host/sdhci-of-k1.c b/drivers/mmc/host/sdhci-of-k1.c
index 585c7eca6ebf253aac466dd37cef029deb63f692..8af117a8e271c04a80d8dc7bb5ce12075652dd7a 100644
--- a/drivers/mmc/host/sdhci-of-k1.c
+++ b/drivers/mmc/host/sdhci-of-k1.c
@@ -15,6 +15,7 @@
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
+#include <linux/pinctrl/consumer.h>
 #include <linux/platform_device.h>
 
 #include "sdhci.h"
@@ -70,6 +71,9 @@
 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 */
@@ -218,6 +222,42 @@ static void spacemit_sdhci_pre_hs400_to_hs200(struct mmc_host *mmc)
 			       SPACEMIT_SDHC_PHY_CTRL_REG);
 }
 
+static void spacemit_sdhci_voltage_switch(struct sdhci_host *host)
+{
+	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
+	struct spacemit_sdhci_host *sdhst = sdhci_pltfm_priv(pltfm_host);
+	struct mmc_ios *ios = &host->mmc->ios;
+	struct pinctrl_state *state;
+	int ret;
+
+	/* Select appropriate pinctrl state based on signal voltage */
+	if (sdhst->pinctrl) {
+		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(host->mmc), "unsupported voltage %d\n",
+				 ios->signal_voltage);
+			return;
+		}
+
+		if (state) {
+			ret = pinctrl_select_state(sdhst->pinctrl, state);
+			if (ret) {
+				dev_warn(mmc_dev(host->mmc),
+					 "failed to select pinctrl state: %d\n", ret);
+				return;
+			}
+			dev_dbg(mmc_dev(host->mmc), "switched to %s pinctrl state\n",
+				ios->signal_voltage == MMC_SIGNAL_VOLTAGE_180 ? "UHS" : "default");
+		}
+	}
+}
+
 static inline int spacemit_sdhci_get_clocks(struct device *dev,
 					    struct sdhci_pltfm_host *pltfm_host)
 {
@@ -242,6 +282,7 @@ static const struct sdhci_ops spacemit_sdhci_ops = {
 	.set_bus_width		= sdhci_set_bus_width,
 	.set_clock		= spacemit_sdhci_set_clock,
 	.set_uhs_signaling	= spacemit_sdhci_set_uhs_signaling,
+	.voltage_switch         = spacemit_sdhci_voltage_switch,
 };
 
 static const struct sdhci_pltfm_data spacemit_sdhci_k1_pdata = {
@@ -293,6 +334,24 @@ static int spacemit_sdhci_probe(struct platform_device *pdev)
 
 	host->mmc->caps |= MMC_CAP_NEED_RSP_BUSY;
 
+	sdhst = sdhci_pltfm_priv(pltfm_host);
+	sdhst->pinctrl = devm_pinctrl_get(dev);
+	if (!IS_ERR(sdhst->pinctrl)) {
+		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);
+	} else {
+		sdhst->pinctrl = NULL;
+		dev_dbg(dev, "pinctrl not available, voltage switching will work without it\n");
+	}
+
 	ret = spacemit_sdhci_get_clocks(dev, pltfm_host);
 	if (ret)
 		goto err_pltfm;

-- 
2.53.0