mmc: sdhci: add quirk SDHCI_QUIRK2_NEED_DELAY_AFTER_INT_CLK_RST

The Atmel sdhci device needs a new quirk. sdhci_set_clock set the Clock
Control Register to 0 before computing the new value and writing it.
It disables the internal clock which causes a reset mecanism. If we
write the new value before this reset mecanism is done, it will prevent
the stabilisation of the internal clock, so a delay is needed. This
delay is about 2-3 cycles of the base clock. To be safe, a 1 ms delay is
used.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci.c

@@ -1160,6 +1160,8 @@ void sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
 	host->mmc->actual_clock = 0;
 
 	sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
+	if (host->quirks2 & SDHCI_QUIRK2_NEED_DELAY_AFTER_INT_CLK_RST)
+		mdelay(1);
 
 	if (clock == 0)
 		return;

drivers/mmc/host/sdhci.h

@@ -412,6 +412,11 @@ struct sdhci_host {
 #define SDHCI_QUIRK2_ACMD23_BROKEN			(1<<14)
 /* Broken Clock divider zero in controller */
 #define SDHCI_QUIRK2_CLOCK_DIV_ZERO_BROKEN		(1<<15)
+/*
+ * When internal clock is disabled, a delay is needed before modifying the
+ * SD clock frequency or enabling back the internal clock.
+ */
+#define SDHCI_QUIRK2_NEED_DELAY_AFTER_INT_CLK_RST	(1<<16)
 
 	int irq;		/* Device IRQ */
 	void __iomem *ioaddr;	/* Mapped address */