[1/2] mmc: let the dma map ops handle bouncing
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Message ID 20190411070948.29564-2-hch@lst.de
State New
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Series
  • [1/2] mmc: let the dma map ops handle bouncing
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Commit Message

Christoph Hellwig April 11, 2019, 7:09 a.m. UTC
Just like we do for all other block drivers.  Especially as the limit
imposed at the moment might be way to pessimistic for iommus.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/mmc/core/queue.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

Comments

Ulf Hansson April 11, 2019, 9 a.m. UTC | #1
Hi Christoph,

On Thu, 11 Apr 2019 at 09:10, Christoph Hellwig <hch@lst.de> wrote:
>
> Just like we do for all other block drivers.  Especially as the limit
> imposed at the moment might be way to pessimistic for iommus.

I would appreciate some information in the changelog, as it's quite
unclear of what this change really means.

>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/mmc/core/queue.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c
> index 7c364a9c4eeb..eb9c0692062c 100644
> --- a/drivers/mmc/core/queue.c
> +++ b/drivers/mmc/core/queue.c
> @@ -354,18 +354,15 @@ static const struct blk_mq_ops mmc_mq_ops = {
>  static void mmc_setup_queue(struct mmc_queue *mq, struct mmc_card *card)
>  {
>         struct mmc_host *host = card->host;
> -       u64 limit = BLK_BOUNCE_HIGH;
>         unsigned block_size = 512;
>
> -       if (mmc_dev(host)->dma_mask && *mmc_dev(host)->dma_mask)
> -               limit = (u64)dma_max_pfn(mmc_dev(host)) << PAGE_SHIFT;
> -
>         blk_queue_flag_set(QUEUE_FLAG_NONROT, mq->queue);
>         blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, mq->queue);
>         if (mmc_can_erase(card))
>                 mmc_queue_setup_discard(mq->queue, card);
>
> -       blk_queue_bounce_limit(mq->queue, limit);
> +       if (!mmc_dev(host)->dma_mask || !*mmc_dev(host)->dma_mask)
> +               blk_queue_bounce_limit(mq->queue, BLK_BOUNCE_HIGH);

So this means we are not going to set a bounce limit for the queue, in
case we have a dma mask.

Why isn't that needed no more? Whats has changed?

>         blk_queue_max_hw_sectors(mq->queue,
>                 min(host->max_blk_count, host->max_req_size / 512));
>         blk_queue_max_segments(mq->queue, host->max_segs);
> --
> 2.20.1
>

Kind regards
Uffe
Christoph Hellwig April 11, 2019, 2:34 p.m. UTC | #2
On Thu, Apr 11, 2019 at 11:00:56AM +0200, Ulf Hansson wrote:
> >         blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, mq->queue);
> >         if (mmc_can_erase(card))
> >                 mmc_queue_setup_discard(mq->queue, card);
> >
> > -       blk_queue_bounce_limit(mq->queue, limit);
> > +       if (!mmc_dev(host)->dma_mask || !*mmc_dev(host)->dma_mask)
> > +               blk_queue_bounce_limit(mq->queue, BLK_BOUNCE_HIGH);
> 
> So this means we are not going to set a bounce limit for the queue, in
> case we have a dma mask.
> 
> Why isn't that needed no more? Whats has changed?

On most architectures it was never needed, the major hold out was x86-32
with PAE.  In general the dma_mask tells the DMA API layer what is
supported, and if the physical addressing doesn't support that it has to
use bounce buffering like swiotlb (or dmabounce on arm32).  A couple
month ago I finally fixes x86-32 to also properly set up swiotlb,
and remove the block layerer bounce buffering that wasn't for highmem
(which is about having a kernel mapping, not addressing), and ISA DMA
(which is not handled like everything else, but we'll get there).
But for some reason I missed mmc back then, so mmc right now is the
only remaining user of address based block layer bouncing.

Patch
diff mbox series

diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c
index 7c364a9c4eeb..eb9c0692062c 100644
--- a/drivers/mmc/core/queue.c
+++ b/drivers/mmc/core/queue.c
@@ -354,18 +354,15 @@  static const struct blk_mq_ops mmc_mq_ops = {
 static void mmc_setup_queue(struct mmc_queue *mq, struct mmc_card *card)
 {
 	struct mmc_host *host = card->host;
-	u64 limit = BLK_BOUNCE_HIGH;
 	unsigned block_size = 512;
 
-	if (mmc_dev(host)->dma_mask && *mmc_dev(host)->dma_mask)
-		limit = (u64)dma_max_pfn(mmc_dev(host)) << PAGE_SHIFT;
-
 	blk_queue_flag_set(QUEUE_FLAG_NONROT, mq->queue);
 	blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, mq->queue);
 	if (mmc_can_erase(card))
 		mmc_queue_setup_discard(mq->queue, card);
 
-	blk_queue_bounce_limit(mq->queue, limit);
+	if (!mmc_dev(host)->dma_mask || !*mmc_dev(host)->dma_mask)
+		blk_queue_bounce_limit(mq->queue, BLK_BOUNCE_HIGH);
 	blk_queue_max_hw_sectors(mq->queue,
 		min(host->max_blk_count, host->max_req_size / 512));
 	blk_queue_max_segments(mq->queue, host->max_segs);