mmc: bounce requests for simple hosts

Some hosts cannot do scatter/gather in hardware. Since not doing sg
is such a big performance hit, we (optionally) bounce the requests
to a simple linear buffer that we hand over to the driver.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

4 files changed, 208 insertions, 15 deletions

diff --git a/drivers/mmc/card/Kconfig b/drivers/mmc/card/Kconfig
index 9320a8c73239..a49cb9737cd8 100644
--- a/drivers/mmc/card/Kconfig
+++ b/drivers/mmc/card/Kconfig
@@ -14,3 +14,21 @@ config MMC_BLOCK
           mount the filesystem. Almost everyone wishing MMC support
           should say Y or M here.
 
+config MMC_BLOCK_BOUNCE
+        bool "Use bounce buffer for simple hosts"
+        depends on MMC_BLOCK
+        default y
+        help
+          SD/MMC is a high latency protocol where it is crucial to
+          send large requests in order to get high performance. Many
+          controllers, however, are restricted to continuous memory
+          (i.e. they can't do scatter-gather), something the kernel
+          rarely can provide.
+
+          Say Y here to help these restricted hosts by bouncing
+          requests back and forth from a large buffer. You will get
+          a big performance gain at the cost of up to 64 KiB of
+          physical memory.
+
+          If unsure, say Y here.
+
diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index 540ff4bea54c..cbd4b6e3e17c 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -262,7 +262,9 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
                 }
 
                 brq.data.sg = mq->sg;
-                brq.data.sg_len = blk_rq_map_sg(req->q, req, brq.data.sg);
+                brq.data.sg_len = mmc_queue_map_sg(mq);
+
+                mmc_queue_bounce_pre(mq);
 
                 if (brq.data.blocks !=
                     (req->nr_sectors >> (md->block_bits - 9))) {
@@ -279,6 +281,9 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
                 }
 
                 mmc_wait_for_req(card->host, &brq.mrq);
+
+                mmc_queue_bounce_post(mq);
+
                 if (brq.cmd.error) {
                         printk(KERN_ERR "%s: error %d sending read/write command\n",
                                req->rq_disk->disk_name, brq.cmd.error);
diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
index dd97bc798409..4fb2089dc690 100644
--- a/drivers/mmc/card/queue.c
+++ b/drivers/mmc/card/queue.c
@@ -17,6 +17,8 @@
 #include <linux/mmc/host.h>
 #include "queue.h"
 
+#define MMC_QUEUE_BOUNCESZ      65536
+
 #define MMC_QUEUE_SUSPENDED     (1 << 0)
 
 /*
@@ -118,6 +120,7 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card, spinlock_t *lock
         struct mmc_host *host = card->host;
         u64 limit = BLK_BOUNCE_HIGH;
         int ret;
+        unsigned int bouncesz;
 
         if (mmc_dev(host)->dma_mask && *mmc_dev(host)->dma_mask)
                 limit = *mmc_dev(host)->dma_mask;
@@ -127,21 +130,61 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card, spinlock_t *lock
         if (!mq->queue)
                 return -ENOMEM;
 
-        blk_queue_prep_rq(mq->queue, mmc_prep_request);
-        blk_queue_bounce_limit(mq->queue, limit);
-        blk_queue_max_sectors(mq->queue, host->max_req_size / 512);
-        blk_queue_max_phys_segments(mq->queue, host->max_phys_segs);
-        blk_queue_max_hw_segments(mq->queue, host->max_hw_segs);
-        blk_queue_max_segment_size(mq->queue, host->max_seg_size);
-
         mq->queue->queuedata = mq;
         mq->req = NULL;
 
-        mq->sg = kmalloc(sizeof(struct scatterlist) * host->max_phys_segs,
-                         GFP_KERNEL);
-        if (!mq->sg) {
-                ret = -ENOMEM;
-                goto cleanup_queue;
+        blk_queue_prep_rq(mq->queue, mmc_prep_request);
+
+#ifdef CONFIG_MMC_BLOCK_BOUNCE
+        if (host->max_hw_segs == 1) {
+                bouncesz = MMC_QUEUE_BOUNCESZ;
+
+                if (bouncesz > host->max_req_size)
+                        bouncesz = host->max_req_size;
+                if (bouncesz > host->max_seg_size)
+                        bouncesz = host->max_seg_size;
+
+                mq->bounce_buf = kmalloc(bouncesz, GFP_KERNEL);
+                if (!mq->bounce_buf) {
+                        printk(KERN_WARNING "%s: unable to allocate "
+                                "bounce buffer\n", mmc_card_name(card));
+                } else {
+                        blk_queue_bounce_limit(mq->queue, BLK_BOUNCE_HIGH);
+                        blk_queue_max_sectors(mq->queue, bouncesz / 512);
+                        blk_queue_max_phys_segments(mq->queue, bouncesz / 512);
+                        blk_queue_max_hw_segments(mq->queue, bouncesz / 512);
+                        blk_queue_max_segment_size(mq->queue, bouncesz);
+
+                        mq->sg = kmalloc(sizeof(struct scatterlist),
+                                GFP_KERNEL);
+                        if (!mq->sg) {
+                                ret = -ENOMEM;
+                                goto free_bounce_buf;
+                        }
+
+                        mq->bounce_sg = kmalloc(sizeof(struct scatterlist) *
+                                bouncesz / 512, GFP_KERNEL);
+                        if (!mq->bounce_sg) {
+                                ret = -ENOMEM;
+                                goto free_sg;
+                        }
+                }
+        }
+#endif
+
+        if (!mq->bounce_buf) {
+                blk_queue_bounce_limit(mq->queue, limit);
+                blk_queue_max_sectors(mq->queue, host->max_req_size / 512);
+                blk_queue_max_phys_segments(mq->queue, host->max_phys_segs);
+                blk_queue_max_hw_segments(mq->queue, host->max_hw_segs);
+                blk_queue_max_segment_size(mq->queue, host->max_seg_size);
+
+                mq->sg = kmalloc(sizeof(struct scatterlist) *
+                        host->max_phys_segs, GFP_KERNEL);
+                if (!mq->sg) {
+                        ret = -ENOMEM;
+                        goto cleanup_queue;
+                }
         }
 
         init_MUTEX(&mq->thread_sem);
@@ -149,14 +192,21 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card, spinlock_t *lock
         mq->thread = kthread_run(mmc_queue_thread, mq, "mmcqd");
         if (IS_ERR(mq->thread)) {
                 ret = PTR_ERR(mq->thread);
-                goto free_sg;
+                goto free_bounce_sg;
         }
 
         return 0;
-
+ free_bounce_sg:
+        if (mq->bounce_sg)
+                kfree(mq->bounce_sg);
+        mq->bounce_sg = NULL;
  free_sg:
         kfree(mq->sg);
         mq->sg = NULL;
+ free_bounce_buf:
+        if (mq->bounce_buf)
+                kfree(mq->bounce_buf);
+        mq->bounce_buf = NULL;
  cleanup_queue:
         blk_cleanup_queue(mq->queue);
         return ret;
@@ -178,9 +228,17 @@ void mmc_cleanup_queue(struct mmc_queue *mq)
         /* Then terminate our worker thread */
         kthread_stop(mq->thread);
 
+        if (mq->bounce_sg)
+                kfree(mq->bounce_sg);
+        mq->bounce_sg = NULL;
+
         kfree(mq->sg);
         mq->sg = NULL;
 
+        if (mq->bounce_buf)
+                kfree(mq->bounce_buf);
+        mq->bounce_buf = NULL;
+
         blk_cleanup_queue(mq->queue);
 
         mq->card = NULL;
@@ -231,3 +289,108 @@ void mmc_queue_resume(struct mmc_queue *mq)
         }
 }
 
+static void copy_sg(struct scatterlist *dst, unsigned int dst_len,
+        struct scatterlist *src, unsigned int src_len)
+{
+        unsigned int chunk;
+        char *dst_buf, *src_buf;
+        unsigned int dst_size, src_size;
+
+        dst_buf = NULL;
+        src_buf = NULL;
+        dst_size = 0;
+        src_size = 0;
+
+        while (src_len) {
+                BUG_ON(dst_len == 0);
+
+                if (dst_size == 0) {
+                        dst_buf = page_address(dst->page) + dst->offset;
+                        dst_size = dst->length;
+                }
+
+                if (src_size == 0) {
+                        src_buf = page_address(src->page) + src->offset;
+                        src_size = src->length;
+                }
+
+                chunk = min(dst_size, src_size);
+
+                memcpy(dst_buf, src_buf, chunk);
+
+                dst_buf += chunk;
+                src_buf += chunk;
+                dst_size -= chunk;
+                src_size -= chunk;
+
+                if (dst_size == 0) {
+                        dst++;
+                        dst_len--;
+                }
+
+                if (src_size == 0) {
+                        src++;
+                        src_len--;
+                }
+        }
+}
+
+unsigned int mmc_queue_map_sg(struct mmc_queue *mq)
+{
+        unsigned int sg_len;
+
+        if (!mq->bounce_buf)
+                return blk_rq_map_sg(mq->queue, mq->req, mq->sg);
+
+        BUG_ON(!mq->bounce_sg);
+
+        sg_len = blk_rq_map_sg(mq->queue, mq->req, mq->bounce_sg);
+
+        mq->bounce_sg_len = sg_len;
+
+        /*
+         * Shortcut in the event we only get a single entry.
+         */
+        if (sg_len == 1) {
+                memcpy(mq->sg, mq->bounce_sg, sizeof(struct scatterlist));
+                return 1;
+        }
+
+        mq->sg[0].page = virt_to_page(mq->bounce_buf);
+        mq->sg[0].offset = offset_in_page(mq->bounce_buf);
+        mq->sg[0].length = 0;
+
+        while (sg_len) {
+                mq->sg[0].length += mq->bounce_sg[sg_len - 1].length;
+                sg_len--;
+        }
+
+        return 1;
+}
+
+void mmc_queue_bounce_pre(struct mmc_queue *mq)
+{
+        if (!mq->bounce_buf)
+                return;
+
+        if (mq->bounce_sg_len == 1)
+                return;
+        if (rq_data_dir(mq->req) != WRITE)
+                return;
+
+        copy_sg(mq->sg, 1, mq->bounce_sg, mq->bounce_sg_len);
+}
+
+void mmc_queue_bounce_post(struct mmc_queue *mq)
+{
+        if (!mq->bounce_buf)
+                return;
+
+        if (mq->bounce_sg_len == 1)
+                return;
+        if (rq_data_dir(mq->req) != READ)
+                return;
+
+        copy_sg(mq->bounce_sg, mq->bounce_sg_len, mq->sg, 1);
+}
+
diff --git a/drivers/mmc/card/queue.h b/drivers/mmc/card/queue.h
index 1590b3f3f1f7..64e66e0d4994 100644
--- a/drivers/mmc/card/queue.h
+++ b/drivers/mmc/card/queue.h
@@ -14,6 +14,9 @@ struct mmc_queue {
         void                    *data;
         struct request_queue    *queue;
         struct scatterlist      *sg;
+        char                    *bounce_buf;
+        struct scatterlist      *bounce_sg;
+        unsigned int            bounce_sg_len;
 };
 
 extern int mmc_init_queue(struct mmc_queue *, struct mmc_card *, spinlock_t *);
@@ -21,4 +24,8 @@ extern void mmc_cleanup_queue(struct mmc_queue *);
 extern void mmc_queue_suspend(struct mmc_queue *);
 extern void mmc_queue_resume(struct mmc_queue *);
 
+extern unsigned int mmc_queue_map_sg(struct mmc_queue *);
+extern void mmc_queue_bounce_pre(struct mmc_queue *);
+extern void mmc_queue_bounce_post(struct mmc_queue *);
+
 #endif