mmc: change .get_ro() callback semantics

Now get_ro() callback must return 0/1 values for its logical states, and
negative errno values in case of error. If particular host instance doesn't
support RO/WP switch, it should return -ENOSYS.

This patch changes some hosts in two ways:

1. Now functions should be smart to not return negative values in
   "RO asserted" case (particularly gpio_ calls could return negative
   values for the outermost GPIOs).

   Also, board code usually passes get_ro() callbacks that directly return
   gpioreg & bit result, so at91_mci, imxmmc, pxamci and mmc_spi's get_ro()
   handlers need take special care when returning platform's values to the
   mmc core.

2. In case of host instance didn't implement get_ro() callback, it should
   really return -ENOSYS and let the mmc core decide what to do about it
   (mmc core thinks the same way as the hosts, so it isn't functional
   change).
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

drivers/mmc/core/sd.c

@@ -494,13 +494,13 @@ static int mmc_sd_init_card(struct mmc_host *host, u32 ocr,
 	 * Check if read-only switch is active.
 	 */
 	if (!oldcard) {
-		if (!host->ops->get_ro) {
+		if (!host->ops->get_ro || host->ops->get_ro(host) < 0) {
 			printk(KERN_WARNING "%s: host does not "
 				"support reading read-only "
 				"switch. assuming write-enable.\n",
 				mmc_hostname(host));
 		} else {
-			if (host->ops->get_ro(host))
+			if (host->ops->get_ro(host) > 0)
 				mmc_card_set_readonly(card);
 		}
 	}

drivers/mmc/host/at91_mci.c

@@ -793,19 +793,15 @@ static irqreturn_t at91_mmc_det_irq(int irq, void *_host)
 
 static int at91_mci_get_ro(struct mmc_host *mmc)
 {
-	int read_only = 0;
 	struct at91mci_host *host = mmc_priv(mmc);
 
-	if (host->board->wp_pin) {
-		read_only = gpio_get_value(host->board->wp_pin);
-		printk(KERN_WARNING "%s: card is %s\n", mmc_hostname(mmc),
-				(read_only ? "read-only" : "read-write") );
-	}
-	else {
-		printk(KERN_WARNING "%s: host does not support reading read-only "
-				"switch.  Assuming write-enable.\n", mmc_hostname(mmc));
-	}
-	return read_only;
+	if (host->board->wp_pin)
+		return !!gpio_get_value(host->board->wp_pin);
+	/*
+	 * Board doesn't support read only detection; let the mmc core
+	 * decide what to do.
+	 */
+	return -ENOSYS;
 }
 
 static const struct mmc_host_ops at91_mci_ops = {

drivers/mmc/host/imxmmc.c

@@ -892,9 +892,12 @@ static int imxmci_get_ro(struct mmc_host *mmc)
 	struct imxmci_host *host = mmc_priv(mmc);
 
 	if (host->pdata && host->pdata->get_ro)
-		return host->pdata->get_ro(mmc_dev(mmc));
-	/* Host doesn't support read only detection so assume writeable */
-	return 0;
+		return !!host->pdata->get_ro(mmc_dev(mmc));
+	/*
+	 * Board doesn't support read only detection; let the mmc core
+	 * decide what to do.
+	 */
+	return -ENOSYS;
 }
 
 

drivers/mmc/host/mmc_spi.c

@@ -1126,9 +1126,12 @@ static int mmc_spi_get_ro(struct mmc_host *mmc)
 	struct mmc_spi_host *host = mmc_priv(mmc);
 
 	if (host->pdata && host->pdata->get_ro)
-		return host->pdata->get_ro(mmc->parent);
-	/* board doesn't support read only detection; assume writeable */
-	return 0;
+		return !!host->pdata->get_ro(mmc->parent);
+	/*
+	 * Board doesn't support read only detection; let the mmc core
+	 * decide what to do.
+	 */
+	return -ENOSYS;
 }
 
 static int mmc_spi_get_cd(struct mmc_host *mmc)

drivers/mmc/host/pxamci.c

@@ -374,9 +374,12 @@ static int pxamci_get_ro(struct mmc_host *mmc)
 	struct pxamci_host *host = mmc_priv(mmc);
 
 	if (host->pdata && host->pdata->get_ro)
-		return host->pdata->get_ro(mmc_dev(mmc));
-	/* Host doesn't support read only detection so assume writeable */
-	return 0;
+		return !!host->pdata->get_ro(mmc_dev(mmc));
+	/*
+	 * Board doesn't support read only detection; let the mmc core
+	 * decide what to do.
+	 */
+	return -ENOSYS;
 }
 
 static void pxamci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)

drivers/mmc/host/wbsd.c

@@ -939,7 +939,7 @@ static int wbsd_get_ro(struct mmc_host *mmc)
 
 	spin_unlock_bh(&host->lock);
 
-	return csr & WBSD_WRPT;
+	return !!(csr & WBSD_WRPT);
 }
 
 static const struct mmc_host_ops wbsd_ops = {

include/linux/mmc/host.h

@@ -58,6 +58,18 @@ struct mmc_host_ops {
 	 *
 	 * Also note that these functions might sleep, so don't call them
 	 * in the atomic contexts!
+	 *
+	 * Return values for the get_ro callback should be:
+	 *   0 for a read/write card
+	 *   1 for a read-only card
+	 *   -ENOSYS when not supported (equal to NULL callback)
+	 *   or a negative errno value when something bad happened
+	 *
+	 * Return values for the get_ro callback should be:
+	 *   0 for a absent card
+	 *   1 for a present card
+	 *   -ENOSYS when not supported (equal to NULL callback)
+	 *   or a negative errno value when something bad happened
 	 */
 	void	(*set_ios)(struct mmc_host *host, struct mmc_ios *ios);
 	int	(*get_ro)(struct mmc_host *host);