mmc: sdhci: Do not disable interrupts while waiting for clock

Disabling interrupts for even a millisecond can cause problems for some
devices. That can happen when sdhci changes clock frequency because it
waits for the clock to become stable under a spin lock.

The spin lock is not necessary here. Anything that is racing with changes
to the I/O state is already broken. The mmc core already provides
synchronization via "claiming" the host.

Although the spin lock probably should be removed from the code paths that
lead to this point, such a patch would touch too much code to be suitable
for stable trees. Consequently, for this patch, just drop the spin lock
while waiting.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Ludovic Desroches <ludovic.desroches@microchip.com>

drivers/mmc/host/sdhci.c

@@ -1362,7 +1362,9 @@ void sdhci_enable_clk(struct sdhci_host *host, u16 clk)
 			return;
 		}
 		timeout--;
-		mdelay(1);
+		spin_unlock_irq(&host->lock);
+		usleep_range(900, 1100);
+		spin_lock_irq(&host->lock);
 	}
 
 	clk |= SDHCI_CLOCK_CARD_EN;