[PATCH v4 05/38] mmc: dw_mmc: Extract divider update to a separate function

[Sam Protsenko]

Extract the clock divider update into dwmci_update_div() function. It's
a procedure recommended in TRM, so it's better to keep it in a dedicated
function to make the code clearer.

While at it also extract the clock control code into a separate routine
to avoid code duplication in dwmci_setup_bus().

No functional change.

Signed-off-by: Sam Protsenko <semen.protsenko at linaro.org>
---
Changes in v4:
  - (none)

Changes in v3:
  - (none)

Changes in v2:
  - Moved CLKSRC after disabling the clock as recommended in TRM, to
    avoid possible glitch
  - Extracted div update into a separate function with corresponding
    comment
  - Changed the patch subject and reworked the commit message

 drivers/mmc/dw_mmc.c | 81 +++++++++++++++++++++++++++-----------------
 1 file changed, 50 insertions(+), 31 deletions(-)

diff --git a/drivers/mmc/dw_mmc.c b/drivers/mmc/dw_mmc.c
index 4a9e57165fbb..b9c14fe6857b 100644
--- a/drivers/mmc/dw_mmc.c
+++ b/drivers/mmc/dw_mmc.c
@@ -410,11 +410,56 @@ static int dwmci_send_cmd(struct mmc *mmc, struct mmc_cmd *cmd,
 	return ret;
 }
 
-static int dwmci_setup_bus(struct dwmci_host *host, u32 freq)
+static int dwmci_control_clken(struct dwmci_host *host, bool on)
 {
-	u32 div, status;
+	const u32 val = on ? DWMCI_CLKEN_ENABLE | DWMCI_CLKEN_LOW_PWR : 0;
+	const u32 cmd_only_clk = DWMCI_CMD_PRV_DAT_WAIT | DWMCI_CMD_UPD_CLK;
 	int timeout = 10000;
+	u32 status;
+
+	dwmci_writel(host, DWMCI_CLKENA, val);
+
+	/* Inform CIU */
+	dwmci_writel(host, DWMCI_CMD, DWMCI_CMD_START | cmd_only_clk);
+	do {
+		status = dwmci_readl(host, DWMCI_CMD);
+		if (timeout-- < 0) {
+			debug("%s: Timeout!\n", __func__);
+			return -ETIMEDOUT;
+		}
+	} while (status & DWMCI_CMD_START);
+
+	return 0;
+}
+
+/*
+ * Update the clock divider.
+ *
+ * To prevent a clock glitch keep the clock stopped during the update of
+ * clock divider and clock source.
+ */
+static int dwmci_update_div(struct dwmci_host *host, u32 div)
+{
+	int ret;
+
+	/* Disable clock */
+	ret = dwmci_control_clken(host, false);
+	if (ret)
+		return ret;
+
+	/* Set clock to desired speed */
+	dwmci_writel(host, DWMCI_CLKDIV, div);
+	dwmci_writel(host, DWMCI_CLKSRC, 0);
+
+	/* Enable clock */
+	return dwmci_control_clken(host, true);
+}
+
+static int dwmci_setup_bus(struct dwmci_host *host, u32 freq)
+{
+	u32 div;
 	unsigned long sclk;
+	int ret;
 
 	if ((freq == host->clock) || (freq == 0))
 		return 0;
@@ -437,35 +482,9 @@ static int dwmci_setup_bus(struct dwmci_host *host, u32 freq)
 	else
 		div = DIV_ROUND_UP(sclk, 2 * freq);
 
-	dwmci_writel(host, DWMCI_CLKENA, 0);
-	dwmci_writel(host, DWMCI_CLKSRC, 0);
-
-	dwmci_writel(host, DWMCI_CLKDIV, div);
-	dwmci_writel(host, DWMCI_CMD, DWMCI_CMD_PRV_DAT_WAIT |
-			DWMCI_CMD_UPD_CLK | DWMCI_CMD_START);
-
-	do {
-		status = dwmci_readl(host, DWMCI_CMD);
-		if (timeout-- < 0) {
-			debug("%s: Timeout!\n", __func__);
-			return -ETIMEDOUT;
-		}
-	} while (status & DWMCI_CMD_START);
-
-	dwmci_writel(host, DWMCI_CLKENA, DWMCI_CLKEN_ENABLE |
-			DWMCI_CLKEN_LOW_PWR);
-
-	dwmci_writel(host, DWMCI_CMD, DWMCI_CMD_PRV_DAT_WAIT |
-			DWMCI_CMD_UPD_CLK | DWMCI_CMD_START);
-
-	timeout = 10000;
-	do {
-		status = dwmci_readl(host, DWMCI_CMD);
-		if (timeout-- < 0) {
-			debug("%s: Timeout!\n", __func__);
-			return -ETIMEDOUT;
-		}
-	} while (status & DWMCI_CMD_START);
+	ret = dwmci_update_div(host, div);
+	if (ret)
+		return ret;
 
 	host->clock = freq;
 
-- 
2.39.2