mmc: sdhci-of-dwcmshc: reduce CIT for better performance

CQHCI_SSC1.CIT indicates to the CQE the polling period to use for
periodic SEND_QUEUE_STATUS (CMD13) polling. Some eMMCs have only one
hardware queue, and CMD13 can only query one slot at a time for data
transmission, which cannot be processed in parallel. Modifying the
CMD13 query interval can increase the query frequency and improve
random write performance.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: shawn1221

drivers/mmc/host/cqhci.h

@@ -93,6 +93,7 @@
 /* send status config 1 */
 #define CQHCI_SSC1			0x40
 #define CQHCI_SSC1_CBC_MASK		GENMASK(19, 16)
+#define CQHCI_SSC1_CIT_MASK		GENMASK(15, 0)
 
 /* send status config 2 */
 #define CQHCI_SSC2			0x44

drivers/mmc/host/sdhci-of-dwcmshc.c

@@ -644,6 +644,11 @@ static void rk35xx_sdhci_cqe_pre_enable(struct mmc_host *mmc)
 	struct dwcmshc_priv *dwc_priv = sdhci_pltfm_priv(pltfm_host);
 	u32 reg;
 
+	/* Set Send Status Command Idle Timer to 10.66us (256 * 1 / 24) */
+	reg = sdhci_readl(host, dwc_priv->vendor_specific_area2 + CQHCI_SSC1);
+	reg = (reg & ~CQHCI_SSC1_CIT_MASK) | 0x0100;
+	sdhci_writel(host, reg, dwc_priv->vendor_specific_area2 + CQHCI_SSC1);
+
 	reg = sdhci_readl(host, dwc_priv->vendor_specific_area2 + CQHCI_CFG);
 	reg |= CQHCI_ENABLE;
 	sdhci_writel(host, reg, dwc_priv->vendor_specific_area2 + CQHCI_CFG);