mmc: sdhci-esdhc-imx: add delay line setting support

The DLL(Delay Line) is newly added to assist in sampling read data.
The DLL provides the ability to programmatically select a quantized
delay (in fractions of the clock period) regardless of on-chip variations
such as process, voltage and temperature (PVT).

This patch adds a user interface to set slave delay line via device tree.
It's usually used in high speed mode like mmc DDR mode when the signal
quality is not good caused by board design, e.g. the signal path is too
long.  User can manually set delay line to find a suitable data sampling
window for card to work properly.

Signed-off-by: Dong Aisheng <b29396@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>

1 files changed, 18 insertions, 0 deletions

diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
index 4b6cd9fa4808..1537e87abe39 100644
--- a/drivers/mmc/host/sdhci-esdhc-imx.c
+++ b/drivers/mmc/host/sdhci-esdhc-imx.c
@@ -46,6 +46,11 @@
 /* Bits 3 and 6 are not SDHCI standard definitions */
 #define  ESDHC_MIX_CTRL_SDHCI_MASK      0xb7
 
+/* dll control register */
+#define ESDHC_DLL_CTRL                  0x60
+#define ESDHC_DLL_OVERRIDE_VAL_SHIFT    9
+#define ESDHC_DLL_OVERRIDE_EN_SHIFT     8
+
 /* tune control register */
 #define ESDHC_TUNE_CTRL_STATUS          0x68
 #define  ESDHC_TUNE_CTRL_STEP           1
@@ -842,6 +847,7 @@ static int esdhc_set_uhs_signaling(struct sdhci_host *host, unsigned int uhs)
 {
         struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
         struct pltfm_imx_data *imx_data = pltfm_host->priv;
+        struct esdhc_platform_data *boarddata = &imx_data->boarddata;
 
         switch (uhs) {
         case MMC_TIMING_UHS_SDR12:
@@ -862,6 +868,15 @@ static int esdhc_set_uhs_signaling(struct sdhci_host *host, unsigned int uhs)
                                 ESDHC_MIX_CTRL_DDREN,
                                 host->ioaddr + ESDHC_MIX_CTRL);
                 imx_data->is_ddr = 1;
+                if (boarddata->delay_line) {
+                        u32 v;
+                        v = boarddata->delay_line <<
+                                ESDHC_DLL_OVERRIDE_VAL_SHIFT |
+                                (1 << ESDHC_DLL_OVERRIDE_EN_SHIFT);
+                        if (is_imx53_esdhc(imx_data))
+                                v <<= 1;
+                        writel(v, host->ioaddr + ESDHC_DLL_CTRL);
+                }
                 break;
         }
 
@@ -924,6 +939,9 @@ sdhci_esdhc_imx_probe_dt(struct platform_device *pdev,
         else
                 boarddata->support_vsel = true;
 
+        if (of_property_read_u32(np, "fsl,delay-line", &boarddata->delay_line))
+                boarddata->delay_line = 0;
+
         return 0;
 }
 #else