mmc: sdhci-of-arasan: Modified SD default speed to 19MHz for ZynqMP

SD standard speed timing was met only at 19MHz and not 25 MHz, that's
why changing driver to 19MHz. The reason for this is when a level shifter
is used on the board, timing was met for standard speed only at 19MHz.
Since this level shifter is commonly required for high speed modes,
the driver is modified to use standard speed of 19Mhz.

Signed-off-by: Manish Narani <manish.narani@xilinx.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/1623753837-21035-2-git-send-email-manish.narani@xilinx.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

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

@@ -159,6 +159,12 @@ struct sdhci_arasan_data {
 /* Controller immediately reports SDHCI_CLOCK_INT_STABLE after enabling the
  * internal clock even when the clock isn't stable */
 #define SDHCI_ARASAN_QUIRK_CLOCK_UNSTABLE BIT(1)
+/*
+ * Some of the Arasan variations might not have timing requirements
+ * met at 25MHz for Default Speed mode, those controllers work at
+ * 19MHz instead
+ */
+#define SDHCI_ARASAN_QUIRK_CLOCK_25_BROKEN BIT(2)
 };
 
 struct sdhci_arasan_of_data {
@@ -290,6 +296,16 @@ static void sdhci_arasan_set_clock(struct sdhci_host *host, unsigned int clock)
 		sdhci_arasan->is_phy_on = false;
 	}
 
+	if (sdhci_arasan->quirks & SDHCI_ARASAN_QUIRK_CLOCK_25_BROKEN) {
+		/*
+		 * Some of the Arasan variations might not have timing
+		 * requirements met at 25MHz for Default Speed mode,
+		 * those controllers work at 19MHz instead.
+		 */
+		if (clock == DEFAULT_SPEED_MAX_DTR)
+			clock = (DEFAULT_SPEED_MAX_DTR * 19) / 25;
+	}
+
 	/* Set the Input and Output Clock Phase Delays */
 	if (clk_data->set_clk_delays)
 		clk_data->set_clk_delays(host);
@@ -1608,6 +1624,8 @@ static int sdhci_arasan_probe(struct platform_device *pdev)
 	if (of_device_is_compatible(np, "xlnx,zynqmp-8.9a")) {
 		host->mmc_host_ops.execute_tuning =
 			arasan_zynqmp_execute_tuning;
+
+		sdhci_arasan->quirks |= SDHCI_ARASAN_QUIRK_CLOCK_25_BROKEN;
 	}
 
 	arasan_dt_parse_clk_phases(dev, &sdhci_arasan->clk_data);