mmc: add support for card-detection polling

Some hosts (and boards that use mmc_spi) do not use interrupts on the CD
line, so they can't trigger mmc_detect_change. We want to poll the card
and see if there was a change. 1 second poll interval seems resonable.

This patch also implements .get_cd() host operation, that could be used
by the hosts that are able to report card-detect status without need to
talk MMC.
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

drivers/mmc/core/core.c

@@ -638,6 +638,9 @@ void mmc_rescan(struct work_struct *work)
 		 */
 		mmc_bus_put(host);
 
+		if (host->ops->get_cd && host->ops->get_cd(host) == 0)
+			goto out;
+
 		mmc_claim_host(host);
 
 		mmc_power_up(host);
@@ -652,7 +655,7 @@ void mmc_rescan(struct work_struct *work)
 		if (!err) {
 			if (mmc_attach_sdio(host, ocr))
 				mmc_power_off(host);
-			return;
+			goto out;
 		}
 
 		/*
@@ -662,7 +665,7 @@ void mmc_rescan(struct work_struct *work)
 		if (!err) {
 			if (mmc_attach_sd(host, ocr))
 				mmc_power_off(host);
-			return;
+			goto out;
 		}
 
 		/*
@@ -672,7 +675,7 @@ void mmc_rescan(struct work_struct *work)
 		if (!err) {
 			if (mmc_attach_mmc(host, ocr))
 				mmc_power_off(host);
-			return;
+			goto out;
 		}
 
 		mmc_release_host(host);
@@ -683,6 +686,9 @@ void mmc_rescan(struct work_struct *work)
 
 		mmc_bus_put(host);
 	}
+out:
+	if (host->caps & MMC_CAP_NEEDS_POLL)
+		mmc_schedule_delayed_work(&host->detect, HZ);
 }
 
 void mmc_start_host(struct mmc_host *host)

include/linux/mmc/host.h

@@ -51,8 +51,18 @@ struct mmc_ios {
 
 struct mmc_host_ops {
 	void	(*request)(struct mmc_host *host, struct mmc_request *req);
+	/*
+	 * Avoid calling these three functions too often or in a "fast path",
+	 * since underlaying controller might implement them in an expensive
+	 * and/or slow way.
+	 *
+	 * Also note that these functions might sleep, so don't call them
+	 * in the atomic contexts!
+	 */
 	void	(*set_ios)(struct mmc_host *host, struct mmc_ios *ios);
 	int	(*get_ro)(struct mmc_host *host);
+	int	(*get_cd)(struct mmc_host *host);
+
 	void	(*enable_sdio_irq)(struct mmc_host *host, int enable);
 };
 
@@ -94,6 +104,7 @@ struct mmc_host {
 #define MMC_CAP_SD_HIGHSPEED	(1 << 3)	/* Can do SD high-speed timing */
 #define MMC_CAP_SDIO_IRQ	(1 << 4)	/* Can signal pending SDIO IRQs */
 #define MMC_CAP_SPI		(1 << 5)	/* Talks only SPI protocols */
+#define MMC_CAP_NEEDS_POLL	(1 << 6)	/* Needs polling for card-detection */
 
 	/* host specific block data */
 	unsigned int		max_seg_size;	/* see blk_queue_max_segment_size */