[MMC] Improve MMC card block size selection

Select a block size for IO based on the read and write block size
combinations, and whether the card supports partial block reads
and/or partial block writes.

If we are able to satisfy block reads but not block writes, mark
the device read only.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

drivers/mmc/mmc.c

@@ -550,6 +550,11 @@ static void mmc_decode_csd(struct mmc_card *card)
 		csd->capacity	  = (1 + m) << (e + 2);
 
 		csd->read_blkbits = UNSTUFF_BITS(resp, 80, 4);
+		csd->read_partial = UNSTUFF_BITS(resp, 79, 1);
+		csd->write_misalign = UNSTUFF_BITS(resp, 78, 1);
+		csd->read_misalign = UNSTUFF_BITS(resp, 77, 1);
+		csd->write_blkbits = UNSTUFF_BITS(resp, 22, 4);
+		csd->write_partial = UNSTUFF_BITS(resp, 21, 1);
 	} else {
 		/*
 		 * We only understand CSD structure v1.1 and v1.2.
@@ -579,6 +584,11 @@ static void mmc_decode_csd(struct mmc_card *card)
 		csd->capacity	  = (1 + m) << (e + 2);
 
 		csd->read_blkbits = UNSTUFF_BITS(resp, 80, 4);
+		csd->read_partial = UNSTUFF_BITS(resp, 79, 1);
+		csd->write_misalign = UNSTUFF_BITS(resp, 78, 1);
+		csd->read_misalign = UNSTUFF_BITS(resp, 77, 1);
+		csd->write_blkbits = UNSTUFF_BITS(resp, 22, 4);
+		csd->write_partial = UNSTUFF_BITS(resp, 21, 1);
 	}
 }
 

drivers/mmc/mmc_block.c

@@ -54,6 +54,7 @@ struct mmc_blk_data {
 
 	unsigned int	usage;
 	unsigned int	block_bits;
+	unsigned int	read_only;
 };
 
 static DECLARE_MUTEX(open_lock);
@@ -85,12 +86,6 @@ static void mmc_blk_put(struct mmc_blk_data *md)
 	up(&open_lock);
 }
 
-static inline int mmc_blk_readonly(struct mmc_card *card)
-{
-	return mmc_card_readonly(card) ||
-	       !(card->csd.cmdclass & CCC_BLOCK_WRITE);
-}
-
 static int mmc_blk_open(struct inode *inode, struct file *filp)
 {
 	struct mmc_blk_data *md;
@@ -102,8 +97,7 @@ static int mmc_blk_open(struct inode *inode, struct file *filp)
 			check_disk_change(inode->i_bdev);
 		ret = 0;
 
-		if ((filp->f_mode & FMODE_WRITE) &&
-			mmc_blk_readonly(md->queue.card))
+		if ((filp->f_mode & FMODE_WRITE) && md->read_only)
 			ret = -EROFS;
 	}
 
@@ -299,6 +293,12 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 
 static unsigned long dev_use[MMC_NUM_MINORS/(8*sizeof(unsigned long))];
 
+static inline int mmc_blk_readonly(struct mmc_card *card)
+{
+	return mmc_card_readonly(card) ||
+	       !(card->csd.cmdclass & CCC_BLOCK_WRITE);
+}
+
 static struct mmc_blk_data *mmc_blk_alloc(struct mmc_card *card)
 {
 	struct mmc_blk_data *md;
@@ -310,64 +310,121 @@ static struct mmc_blk_data *mmc_blk_alloc(struct mmc_card *card)
 	__set_bit(devidx, dev_use);
 
 	md = kmalloc(sizeof(struct mmc_blk_data), GFP_KERNEL);
-	if (md) {
-		memset(md, 0, sizeof(struct mmc_blk_data));
+	if (!md) {
+		ret = -ENOMEM;
+		goto out;
+	}
 
-		md->disk = alloc_disk(1 << MMC_SHIFT);
-		if (md->disk == NULL) {
-			kfree(md);
-			md = ERR_PTR(-ENOMEM);
-			goto out;
-		}
+	memset(md, 0, sizeof(struct mmc_blk_data));
 
-		spin_lock_init(&md->lock);
-		md->usage = 1;
+	/*
+	 * Set the read-only status based on the supported commands
+	 * and the write protect switch.
+	 */
+	md->read_only = mmc_blk_readonly(card);
 
-		ret = mmc_init_queue(&md->queue, card, &md->lock);
-		if (ret) {
-			put_disk(md->disk);
-			kfree(md);
-			md = ERR_PTR(ret);
-			goto out;
+	/*
+	 * Figure out a workable block size.  MMC cards have:
+	 *  - two block sizes, one for read and one for write.
+	 *  - may support partial reads and/or writes
+	 *    (allows block sizes smaller than specified)
+	 */
+	md->block_bits = card->csd.read_blkbits;
+	if (card->csd.write_blkbits != card->csd.read_blkbits) {
+		if (card->csd.write_blkbits < card->csd.read_blkbits &&
+		    card->csd.read_partial) {
+			/*
+			 * write block size is smaller than read block
+			 * size, but we support partial reads, so choose
+			 * the smaller write block size.
+			 */
+			md->block_bits = card->csd.write_blkbits;
+		} else if (card->csd.write_blkbits > card->csd.read_blkbits &&
+			   card->csd.write_partial) {
+			/*
+			 * read block size is smaller than write block
+			 * size, but we support partial writes.  Use read
+			 * block size.
+			 */
+		} else {
+			/*
+			 * We don't support this configuration for writes.
+			 */
+			printk(KERN_ERR "%s: unable to select block size for "
+				"writing (rb%u wb%u rp%u wp%u)\n",
+				md->disk->disk_name,
+				1 << card->csd.read_blkbits,
+				1 << card->csd.write_blkbits,
+				card->csd.read_partial,
+				card->csd.write_partial);
+			md->read_only = 1;
 		}
-		md->queue.prep_fn = mmc_blk_prep_rq;
-		md->queue.issue_fn = mmc_blk_issue_rq;
-		md->queue.data = md;
+	}
 
-		md->disk->major	= major;
-		md->disk->first_minor = devidx << MMC_SHIFT;
-		md->disk->fops = &mmc_bdops;
-		md->disk->private_data = md;
-		md->disk->queue = md->queue.queue;
-		md->disk->driverfs_dev = &card->dev;
+	/*
+	 * Refuse to allow block sizes smaller than 512 bytes.
+	 */
+	if (md->block_bits < 9) {
+		printk(KERN_ERR "%s: unable to support block size %u\n",
+			mmc_card_id(card), 1 << md->block_bits);
+		ret = -EINVAL;
+		goto err_kfree;
+	}
 
-		/*
-		 * As discussed on lkml, GENHD_FL_REMOVABLE should:
-		 *
-		 * - be set for removable media with permanent block devices
-		 * - be unset for removable block devices with permanent media
-		 *
-		 * Since MMC block devices clearly fall under the second
-		 * case, we do not set GENHD_FL_REMOVABLE.  Userspace
-		 * should use the block device creation/destruction hotplug
-		 * messages to tell when the card is present.
-		 */
+	md->disk = alloc_disk(1 << MMC_SHIFT);
+	if (md->disk == NULL) {
+		ret = -ENOMEM;
+		goto err_kfree;
+	}
 
-		sprintf(md->disk->disk_name, "mmcblk%d", devidx);
-		sprintf(md->disk->devfs_name, "mmc/blk%d", devidx);
+	spin_lock_init(&md->lock);
+	md->usage = 1;
 
-		md->block_bits = card->csd.read_blkbits;
+	ret = mmc_init_queue(&md->queue, card, &md->lock);
+	if (ret)
+		goto err_putdisk;
 
-		blk_queue_hardsect_size(md->queue.queue, 1 << md->block_bits);
+	md->queue.prep_fn = mmc_blk_prep_rq;
+	md->queue.issue_fn = mmc_blk_issue_rq;
+	md->queue.data = md;
 
-		/*
-		 * The CSD capacity field is in units of read_blkbits.
-		 * set_capacity takes units of 512 bytes.
-		 */
-		set_capacity(md->disk, card->csd.capacity << (card->csd.read_blkbits - 9));
-	}
- out:
+	md->disk->major	= major;
+	md->disk->first_minor = devidx << MMC_SHIFT;
+	md->disk->fops = &mmc_bdops;
+	md->disk->private_data = md;
+	md->disk->queue = md->queue.queue;
+	md->disk->driverfs_dev = &card->dev;
+
+	/*
+	 * As discussed on lkml, GENHD_FL_REMOVABLE should:
+	 *
+	 * - be set for removable media with permanent block devices
+	 * - be unset for removable block devices with permanent media
+	 *
+	 * Since MMC block devices clearly fall under the second
+	 * case, we do not set GENHD_FL_REMOVABLE.  Userspace
+	 * should use the block device creation/destruction hotplug
+	 * messages to tell when the card is present.
+	 */
+
+	sprintf(md->disk->disk_name, "mmcblk%d", devidx);
+	sprintf(md->disk->devfs_name, "mmc/blk%d", devidx);
+
+	blk_queue_hardsect_size(md->queue.queue, 1 << md->block_bits);
+
+	/*
+	 * The CSD capacity field is in units of read_blkbits.
+	 * set_capacity takes units of 512 bytes.
+	 */
+	set_capacity(md->disk, card->csd.capacity << (card->csd.read_blkbits - 9));
 	return md;
+
+ err_putdisk:
+	put_disk(md->disk);
+ err_kfree:
+	kfree(md);
+ out:
+	return ERR_PTR(ret);
 }
 
 static int
@@ -403,12 +460,6 @@ static int mmc_blk_probe(struct mmc_card *card)
 	if (!(card->csd.cmdclass & CCC_BLOCK_READ))
 		return -ENODEV;
 
-	if (card->csd.read_blkbits < 9) {
-		printk(KERN_WARNING "%s: read blocksize too small (%u)\n",
-			mmc_card_id(card), 1 << card->csd.read_blkbits);
-		return -ENODEV;
-	}
-
 	md = mmc_blk_alloc(card);
 	if (IS_ERR(md))
 		return PTR_ERR(md);
@@ -419,7 +470,7 @@ static int mmc_blk_probe(struct mmc_card *card)
 
 	printk(KERN_INFO "%s: %s %s %luKiB %s\n",
 		md->disk->disk_name, mmc_card_id(card), mmc_card_name(card),
-		get_capacity(md->disk) >> 1, mmc_blk_readonly(card)?"(ro)":"");
+		get_capacity(md->disk) >> 1, md->read_only ? "(ro)" : "");
 
 	mmc_set_drvdata(card, md);
 	add_disk(md->disk);

include/linux/mmc/card.h

@@ -30,7 +30,12 @@ struct mmc_csd {
 	unsigned int		tacc_ns;
 	unsigned int		max_dtr;
 	unsigned int		read_blkbits;
+	unsigned int		write_blkbits;
 	unsigned int		capacity;
+	unsigned int		read_partial:1,
+				read_misalign:1,
+				write_partial:1
+				write_misalign:1;
 };
 
 struct sd_scr {