block: ataflop: fix breakage introduced at blk-mq refactoring

Refactoring of the Atari floppy driver when converting to blk-mq
has broken the state machine in not-so-subtle ways:

finish_fdc() must be called when operations on the floppy device
have completed. This is crucial in order to relase the ST-DMA
lock, which protects against concurrent access to the ST-DMA
controller by other drivers (some DMA related, most just related
to device register access - broken beyond compare, I know).

When rewriting the driver's old do_request() function, the fact
that finish_fdc() was called only when all queued requests had
completed appears to have been overlooked. Instead, the new
request function calls finish_fdc() immediately after the last
request has been queued. finish_fdc() executes a dummy seek after
most requests, and this overwrites the state machine's interrupt
hander that was set up to wait for completion of the read/write
request just prior. To make matters worse, finish_fdc() is called
before device interrupts are re-enabled, making certain that the
read/write interupt is missed.

Shifting the finish_fdc() call into the read/write request
completion handler ensures the driver waits for the request to
actually complete. With a queue depth of 2, we won't see long
request sequences, so calling finish_fdc() unconditionally just
adds a little overhead for the dummy seeks, and keeps the code
simple.

While we're at it, kill ataflop_commit_rqs() which does nothing
but run finish_fdc() unconditionally, again likely wiping out an
in-flight request.
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
Fixes: 6ec3938c ("ataflop: convert to blk-mq")
CC: linux-block@vger.kernel.org
CC: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Link: https://lore.kernel.org/r/20211019061321.26425-1-schmitzmic@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/ataflop.c

@@ -655,9 +655,6 @@ static inline void copy_buffer(void *from, void *to)
 		*p2++ = *p1++;
 }
 
-  
-  
-
 /* General Interrupt Handling */
 
 static void (*FloppyIRQHandler)( int status ) = NULL;
@@ -1230,6 +1227,7 @@ static void fd_rwsec_done1(int status)
 	}
 	else {
 		/* all sectors finished */
+		finish_fdc();
 		fd_end_request_cur(BLK_STS_OK);
 	}
 	return;
@@ -1477,15 +1475,6 @@ static void setup_req_params( int drive )
 			ReqTrack, ReqSector, (unsigned long)ReqData ));
 }
 
-static void ataflop_commit_rqs(struct blk_mq_hw_ctx *hctx)
-{
-	spin_lock_irq(&ataflop_lock);
-	atari_disable_irq(IRQ_MFP_FDC);
-	finish_fdc();
-	atari_enable_irq(IRQ_MFP_FDC);
-	spin_unlock_irq(&ataflop_lock);
-}
-
 static blk_status_t ataflop_queue_rq(struct blk_mq_hw_ctx *hctx,
 				     const struct blk_mq_queue_data *bd)
 {
@@ -1493,6 +1482,8 @@ static blk_status_t ataflop_queue_rq(struct blk_mq_hw_ctx *hctx,
 	int drive = floppy - unit;
 	int type = floppy->type;
 
+	DPRINT(("Queue request: drive %d type %d last %d\n", drive, type, bd->last));
+
 	spin_lock_irq(&ataflop_lock);
 	if (fd_request) {
 		spin_unlock_irq(&ataflop_lock);
@@ -1552,8 +1543,6 @@ static blk_status_t ataflop_queue_rq(struct blk_mq_hw_ctx *hctx,
 	setup_req_params( drive );
 	do_fd_action( drive );
 
-	if (bd->last)
-		finish_fdc();
 	atari_enable_irq( IRQ_MFP_FDC );
 
 out:
@@ -1964,7 +1953,6 @@ static const struct block_device_operations floppy_fops = {
 
 static const struct blk_mq_ops ataflop_mq_ops = {
 	.queue_rq = ataflop_queue_rq,
-	.commit_rqs = ataflop_commit_rqs,
 };
 
 static int ataflop_alloc_disk(unsigned int drive, unsigned int type)