[PATCH v2 17/32] swim: Convert to blocking queue

[Finn Thain <fthain@linux-m68k.org>]

These drives are slow: completing a request can take hundreds of
milliseconds. Delays are managed by disabling interrupts judiciously and
sleeping opportunistically.

As of commit e3896d77b702 ("swim: convert to blk-mq"), a spinlock is
taken in irq mode as soon as a request is issued. That lock is held for
the duration of the request. Hence the driver sleeps while holding the
lock which is forbidden.

Adopt BLK_MQ_F_BLOCKING and remove the spinlock. Use a mutex to serialize
requests from the two request queues. (The chip cannot simultaneously
process requests on both internal and external drive.)

Cc: Omar Sandoval <osandov@fb.com>
Fixes: e3896d77b702 ("swim: convert to blk-mq")
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
---
 drivers/block/swim.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/block/swim.c b/drivers/block/swim.c
index 33374498d621..8c8b157e2d74 100644
--- a/drivers/block/swim.c
+++ b/drivers/block/swim.c
@@ -211,7 +211,6 @@ enum head {
 
 struct swim_priv {
 	struct swim __iomem *base;
-	spinlock_t lock;
 	int floppy_count;
 	struct floppy_state unit[FD_MAX_UNIT];
 };
@@ -537,12 +536,10 @@ static blk_status_t swim_queue_rq(struct blk_mq_hw_ctx *hctx,
 				  const struct blk_mq_queue_data *bd)
 {
 	struct floppy_state *fs = hctx->queue->queuedata;
-	struct swim_priv *swd = fs->swd;
 	struct request *req = bd->rq;
 	blk_status_t err;
 
-	if (!spin_trylock_irq(&swd->lock))
-		return BLK_STS_DEV_RESOURCE;
+	mutex_lock(&swim_mutex);
 
 	blk_mq_start_request(req);
 
@@ -560,7 +557,7 @@ static blk_status_t swim_queue_rq(struct blk_mq_hw_ctx *hctx,
 
 	err = BLK_STS_OK;
 out:
-	spin_unlock_irq(&swd->lock);
+	mutex_unlock(&swim_mutex);
 	return err;
 
 }
@@ -841,11 +838,9 @@ static int swim_floppy_init(struct platform_device *pdev)
 		return -EBUSY;
 	}
 
-	spin_lock_init(&swd->lock);
-
 	for (drive = 0; drive < swd->floppy_count; drive++) {
 		err = blk_mq_alloc_sq_tag_set(&swd->unit[drive].tag_set,
-				&swim_mq_ops, 2, 0);
+				&swim_mq_ops, 2, BLK_MQ_F_BLOCKING);
 		if (err)
 			goto exit_put_disks;
 
-- 
2.52.0