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>

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 */