mmc: core: Prevent too long response times for suspend

While trying to suspend the mmc host there could still be
ongoing requests that we need to wait for. At the same time
a device driver must respond to a suspend request rather quickly.

Instead of potentially wait "forever" by claiming the host we now
"try" to claim the host instead. If it fails, -EBUSY is returned.
Signed-off-by: Ulf Hansson <ulf.hansson@stericsson.com>
Reviewed-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/core.c

@@ -2294,21 +2294,33 @@ int mmc_suspend_host(struct mmc_host *host)
 
 	mmc_bus_get(host);
 	if (host->bus_ops && !host->bus_dead) {
-		if (host->bus_ops->suspend)
-			err = host->bus_ops->suspend(host);
-		if (err == -ENOSYS || !host->bus_ops->resume) {
-			/*
-			 * We simply "remove" the card in this case.
-			 * It will be redetected on resume.
-			 */
-			if (host->bus_ops->remove)
-				host->bus_ops->remove(host);
-			mmc_claim_host(host);
-			mmc_detach_bus(host);
-			mmc_power_off(host);
-			mmc_release_host(host);
-			host->pm_flags = 0;
-			err = 0;
+
+		/*
+		 * A long response time is not acceptable for device drivers
+		 * when doing suspend. Prevent mmc_claim_host in the suspend
+		 * sequence, to potentially wait "forever" by trying to
+		 * pre-claim the host.
+		 */
+		if (mmc_try_claim_host(host)) {
+			if (host->bus_ops->suspend)
+				err = host->bus_ops->suspend(host);
+			if (err == -ENOSYS || !host->bus_ops->resume) {
+				/*
+				 * We simply "remove" the card in this case.
+				 * It will be redetected on resume.
+				 */
+				if (host->bus_ops->remove)
+					host->bus_ops->remove(host);
+				mmc_claim_host(host);
+				mmc_detach_bus(host);
+				mmc_power_off(host);
+				mmc_release_host(host);
+				host->pm_flags = 0;
+				err = 0;
+			}
+			mmc_do_release_host(host);
+		} else {
+			err = -EBUSY;
 		}
 	}
 	mmc_bus_put(host);