[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>

2 files changed, 123 insertions, 62 deletions

diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index eb41391e06e9..6696f71363b9 100644
--- a/drivers/mmc/mmc.c
+++ b/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);
         }
 }
 
diff --git a/drivers/mmc/mmc_block.c b/drivers/mmc/mmc_block.c
index abcf19116d70..b9837cc5b9ac 100644
--- a/drivers/mmc/mmc_block.c
+++ b/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);