[PATCH v2 5/7] mmc: meson-gx: avoid clock glitch when switching to DDR modes

[Jerome Brunet]

Activating DDR in the Amlogic mmc controller, among other things, will
divide the output clock by 2. So by activating it with clock on, we are
creating a glitch on the output.

Instead, let's deal with DDR when the clock output is off, when setting
the clock.

Signed-off-by: Jerome Brunet <jbrunet@xxxxxxxxxxxx>
---
 drivers/mmc/host/meson-gx-mmc.c | 73 +++++++++++++++++++--------------
 1 file changed, 43 insertions(+), 30 deletions(-)

diff --git a/drivers/mmc/host/meson-gx-mmc.c b/drivers/mmc/host/meson-gx-mmc.c
index 118f09da8dfb..0454021c9ff5 100644
--- a/drivers/mmc/host/meson-gx-mmc.c
+++ b/drivers/mmc/host/meson-gx-mmc.c
@@ -169,6 +169,7 @@ struct meson_host {
 	struct clk *rx_clk;
 	struct clk *tx_clk;
 	unsigned long req_rate;
+	bool ddr;
 
 	struct pinctrl *pinctrl;
 	struct pinctrl_state *pins_default;
@@ -384,16 +385,6 @@ static void meson_mmc_post_req(struct mmc_host *mmc, struct mmc_request *mrq,
 			     mmc_get_dma_dir(data));
 }
 
-static bool meson_mmc_timing_is_ddr(struct mmc_ios *ios)
-{
-	if (ios->timing == MMC_TIMING_MMC_DDR52 ||
-	    ios->timing == MMC_TIMING_UHS_DDR50 ||
-	    ios->timing == MMC_TIMING_MMC_HS400)
-		return true;
-
-	return false;
-}
-
 /*
  * Gating the clock on this controller is tricky.  It seems the mmc clock
  * is also used by the controller.  It may crash during some operation if the
@@ -430,36 +421,41 @@ static void meson_mmc_clk_ungate(struct meson_host *host)
 	writel(cfg, host->regs + SD_EMMC_CFG);
 }
 
-static int meson_mmc_clk_set(struct meson_host *host, struct mmc_ios *ios)
+static int meson_mmc_clk_set(struct meson_host *host, unsigned long rate,
+			     bool ddr)
 {
 	struct mmc_host *mmc = host->mmc;
-	unsigned long rate = ios->clock;
 	int ret;
 	u32 cfg;
 
-	/* DDR modes require higher module clock */
-	if (meson_mmc_timing_is_ddr(ios))
-		rate <<= 1;
-
 	/* Same request - bail-out */
-	if (host->req_rate == rate)
+	if (host->ddr == ddr && host->req_rate == rate)
 		return 0;
 
 	/* stop clock */
 	meson_mmc_clk_gate(host);
 	host->req_rate = 0;
+	mmc->actual_clock = 0;
 
-	if (!rate) {
-		mmc->actual_clock = 0;
-		/* return with clock being stopped */
+	/* return with clock being stopped */
+	if (!rate)
 		return 0;
-	}
 
 	/* Stop the clock during rate change to avoid glitches */
 	cfg = readl(host->regs + SD_EMMC_CFG);
 	cfg |= CFG_STOP_CLOCK;
 	writel(cfg, host->regs + SD_EMMC_CFG);
 
+	if (ddr) {
+		/* DDR modes require higher module clock */
+		rate <<= 1;
+		cfg |= CFG_DDR;
+	} else {
+		cfg &= ~CFG_DDR;
+	}
+	writel(cfg, host->regs + SD_EMMC_CFG);
+	host->ddr = ddr;
+
 	ret = clk_set_rate(host->mmc_clk, rate);
 	if (ret) {
 		dev_err(host->dev, "Unable to set cfg_div_clk to %lu. ret=%d\n",
@@ -471,12 +467,14 @@ static int meson_mmc_clk_set(struct meson_host *host, struct mmc_ios *ios)
 	mmc->actual_clock = clk_get_rate(host->mmc_clk);
 
 	/* We should report the real output frequency of the controller */
-	if (meson_mmc_timing_is_ddr(ios))
+	if (ddr) {
+		host->req_rate >>= 1;
 		mmc->actual_clock >>= 1;
+	}
 
 	dev_dbg(host->dev, "clk rate: %u Hz\n", mmc->actual_clock);
-	if (ios->clock != mmc->actual_clock)
-		dev_dbg(host->dev, "requested rate was %u\n", ios->clock);
+	if (rate != mmc->actual_clock)
+		dev_dbg(host->dev, "requested rate was %lu\n", rate);
 
 	/* (re)start clock */
 	meson_mmc_clk_ungate(host);
@@ -750,6 +748,25 @@ static int meson_mmc_execute_tuning(struct mmc_host *mmc, u32 opcode)
 	return meson_mmc_clk_phase_tuning(mmc, opcode, host->rx_clk);
 }
 
+static int meson_mmc_prepare_ios_clock(struct meson_host *host,
+				       struct mmc_ios *ios)
+{
+	bool ddr;
+
+	switch (ios->timing) {
+	case MMC_TIMING_MMC_DDR52:
+	case MMC_TIMING_UHS_DDR50:
+		ddr = true;
+		break;
+
+	default:
+		ddr = false;
+		break;
+	}
+
+	return meson_mmc_clk_set(host, ios->clock, ddr);
+}
+
 static void meson_mmc_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 {
 	struct meson_host *host = mmc_priv(mmc);
@@ -818,16 +835,12 @@ static void meson_mmc_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 	val = readl(host->regs + SD_EMMC_CFG);
 	val &= ~CFG_BUS_WIDTH_MASK;
 	val |= FIELD_PREP(CFG_BUS_WIDTH_MASK, bus_width);
+	writel(val, host->regs + SD_EMMC_CFG);
 
-	val &= ~CFG_DDR;
-	if (meson_mmc_timing_is_ddr(ios))
-		val |= CFG_DDR;
-
-	err = meson_mmc_clk_set(host, ios);
+	err = meson_mmc_prepare_ios_clock(host, ios);
 	if (err)
 		dev_err(host->dev, "Failed to set clock: %d\n,", err);
 
-	writel(val, host->regs + SD_EMMC_CFG);
 	dev_dbg(host->dev, "SD_EMMC_CFG:  0x%08x\n", val);
 }
 
-- 
2.20.1