[PATCH 3/6] mmc: sdhci-esdhc-imx: widen auto-tuning window for standard tuning

[ziniu . wang_1]

From: Haibo Chen <haibo.chen@xxxxxxx>

Expand the auto-tuning window width from 2 to 3 for standard tuning to
account for sampling point shifts caused by temperature change. This change
is based on hardware recommendation, providing 50% more margin for the
auto-tuning logic to locate valid sampling points.

Signed-off-by: Haibo Chen <haibo.chen@xxxxxxx>
Signed-off-by: Luke Wang <ziniu.wang_1@xxxxxxx>
---
 drivers/mmc/host/sdhci-esdhc-imx.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
index 8528aa6adf02..d91b65439544 100644
--- a/drivers/mmc/host/sdhci-esdhc-imx.c
+++ b/drivers/mmc/host/sdhci-esdhc-imx.c
@@ -108,6 +108,7 @@
 
 #define ESDHC_TUNING_CTRL		0xcc
 #define ESDHC_STD_TUNING_EN		(1 << 24)
+#define ESDHC_TUNING_WINDOW_MASK	GENMASK(22, 20)
 /* NOTE: the minimum valid tuning start tap for mx6sl is 1 */
 #define ESDHC_TUNING_START_TAP_DEFAULT	0x1
 #define ESDHC_TUNING_START_TAP_MASK	0x7f
@@ -209,6 +210,8 @@
 /* The IP does not have GPIO CD wake capabilities */
 #define ESDHC_FLAG_SKIP_CD_WAKE		BIT(18)
 
+#define ESDHC_AUTO_TUNING_WINDOW	3
+
 enum wp_types {
 	ESDHC_WP_NONE,		/* no WP, neither controller nor gpio */
 	ESDHC_WP_CONTROLLER,	/* mmc controller internal WP */
@@ -1560,6 +1563,16 @@ static void sdhci_esdhc_imx_hwinit(struct sdhci_host *host)
 					<< ESDHC_TUNING_STEP_SHIFT;
 			}
 
+			/*
+			 * Config the tuning window to the hardware suggested value 3.
+			 * This tuning window is used for auto tuning logic. The default
+			 * tuning window is 2, here change to 3 make the window a bit
+			 * wider, give auto tuning enough space to handle the sample
+			 * point shift cause by temperature change.
+			 */
+			 tmp &= ~ESDHC_TUNING_WINDOW_MASK;
+			 tmp |= FIELD_PREP(ESDHC_TUNING_WINDOW_MASK, ESDHC_AUTO_TUNING_WINDOW);
+
 			/* Disable the CMD CRC check for tuning, if not, need to
 			 * add some delay after every tuning command, because
 			 * hardware standard tuning logic will directly go to next
-- 
2.34.1