mmc: sdhci-brcmstb: Enable Clock Gating to save power

Enabling this feature will allow the controller to stop the bus
clock when the bus is idle. The feature is not part of the standard
and is unique to newer Arasan cores and is enabled with a bit in a
vendor specific register. This feature will only be enabled for
non-removable devices because they don't switch the voltage and
clock gating breaks SD Card volatge switching.

Signed-off-by: Al Cooper <alcooperx@gmail.com>
Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20220427180853.35970-3-kdasu.kdev@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: alcooper

drivers/mmc/host/sdhci-brcmstb.c

@@ -17,11 +17,14 @@
 
 #define SDHCI_VENDOR 0x78
 #define  SDHCI_VENDOR_ENHANCED_STRB 0x1
+#define  SDHCI_VENDOR_GATE_SDCLK_EN 0x2
 
 #define BRCMSTB_MATCH_FLAGS_NO_64BIT		BIT(0)
 #define BRCMSTB_MATCH_FLAGS_BROKEN_TIMEOUT	BIT(1)
+#define BRCMSTB_MATCH_FLAGS_HAS_CLOCK_GATE	BIT(2)
 
 #define BRCMSTB_PRIV_FLAGS_HAS_CQE		BIT(0)
+#define BRCMSTB_PRIV_FLAGS_GATE_CLOCK		BIT(1)
 
 #define SDHCI_ARASAN_CQE_BASE_ADDR		0x200
 
@@ -36,6 +39,27 @@ struct brcmstb_match_priv {
 	const unsigned int flags;
 };
 
+static inline void enable_clock_gating(struct sdhci_host *host)
+{
+	u32 reg;
+
+	reg = sdhci_readl(host, SDHCI_VENDOR);
+	reg |= SDHCI_VENDOR_GATE_SDCLK_EN;
+	sdhci_writel(host, reg, SDHCI_VENDOR);
+}
+
+void brcmstb_reset(struct sdhci_host *host, u8 mask)
+{
+	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
+	struct sdhci_brcmstb_priv *priv = sdhci_pltfm_priv(pltfm_host);
+
+	sdhci_reset(host, mask);
+
+	/* Reset will clear this, so re-enable it */
+	if (priv->flags & BRCMSTB_PRIV_FLAGS_GATE_CLOCK)
+		enable_clock_gating(host);
+}
+
 static void sdhci_brcmstb_hs400es(struct mmc_host *mmc, struct mmc_ios *ios)
 {
 	struct sdhci_host *host = mmc_priv(mmc);
@@ -131,7 +155,7 @@ static struct sdhci_ops sdhci_brcmstb_ops = {
 static struct sdhci_ops sdhci_brcmstb_ops_7216 = {
 	.set_clock = sdhci_brcmstb_set_clock,
 	.set_bus_width = sdhci_set_bus_width,
-	.reset = sdhci_reset,
+	.reset = brcmstb_reset,
 	.set_uhs_signaling = sdhci_brcmstb_set_uhs_signaling,
 };
 
@@ -147,6 +171,7 @@ static struct brcmstb_match_priv match_priv_7445 = {
 };
 
 static const struct brcmstb_match_priv match_priv_7216 = {
+	.flags = BRCMSTB_MATCH_FLAGS_HAS_CLOCK_GATE,
 	.hs400es = sdhci_brcmstb_hs400es,
 	.ops = &sdhci_brcmstb_ops_7216,
 };
@@ -273,6 +298,14 @@ static int sdhci_brcmstb_probe(struct platform_device *pdev)
 	if (res)
 		goto err;
 
+	/*
+	 * Automatic clock gating does not work for SD cards that may
+	 * voltage switch so only enable it for non-removable devices.
+	 */
+	if ((match_priv->flags & BRCMSTB_MATCH_FLAGS_HAS_CLOCK_GATE) &&
+	    (host->mmc->caps & MMC_CAP_NONREMOVABLE))
+		priv->flags |= BRCMSTB_PRIV_FLAGS_GATE_CLOCK;
+
 	/*
 	 * If the chip has enhanced strobe and it's enabled, add
 	 * callback