On Tue, 2014-02-11 at 17:28 +0000, Russell King wrote:
> We must use a 64-bit for this, otherwise overflowed bits get lost, and
> that can result in a lower than intended value set.
>
> Fixes: 8e0cb8a1f6ac ("ARM: 7797/1: mmc: Use dma_max_pfn(dev) helper for bounce_limit calculations")
> Fixes: 7d35496dd982 ("ARM: 7796/1: scsi: Use dma_max_pfn(dev) helper for bounce_limit calculations")
> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
> ---
> While poking about with the Cubox-i4 and investigating why my UHS-1
> SD card wasn't achieving its full potential, I came across a slight
> problem... the SDHCI host sets a mask of 0xffffffff, but with the
> start of memory at pfn 0x10000, the blk code sees this when setting
> the bounce limit:
>
> max addr 0x0ffff000 bounce limit 0xffff dma 1
>
> and this results in the bounce functions appearing in the profile:
>
> 00000000c00f8b70 copy_to_high_bio_irq 1139 2.5886
> 00000000c00f8d28 bounce_end_io 12 0.0714
> 00000000c00f8dd0 bounce_end_io_read_isa 8 0.1053
>
> which, compared to the cost of copying the data to userland and
> request handling, this is quite significant:
>
> 00000000c04b1794 sdhci_request 268 0.5447
> 00000000c02d0740 __copy_to_user_std 398 0.4252
>
> With this calculation fixed, we avoid the bouncing code entirely.
>
> max addr 0x10ffff000 bounce limit 0x10ffff dma 0
>
> drivers/mmc/card/queue.c | 2 +-
> drivers/scsi/scsi_lib.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
> index 357bbc54fe4b..3e049c13429c 100644
> --- a/drivers/mmc/card/queue.c
> +++ b/drivers/mmc/card/queue.c
> @@ -197,7 +197,7 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card,
> struct mmc_queue_req *mqrq_prev = &mq->mqrq[1];
>
> if (mmc_dev(host)->dma_mask && *mmc_dev(host)->dma_mask)
> - limit = dma_max_pfn(mmc_dev(host)) << PAGE_SHIFT;
> + limit = (u64)dma_max_pfn(mmc_dev(host)) << PAGE_SHIFT;
>
> mq->card = card;
> mq->queue = blk_init_queue(mmc_request_fn, lock);
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 7bd7f0d5f050..62ec84b42e31 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1684,7 +1684,7 @@ u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
>
> host_dev = scsi_get_device(shost);
> if (host_dev && host_dev->dma_mask)
> - bounce_limit = dma_max_pfn(host_dev) << PAGE_SHIFT;
> + bounce_limit = (u64)dma_max_pfn(host_dev) << PAGE_SHIFT;
This doesn't really look like the right fix. You replaced dev->dma_mask
with a calculation on dev_max_pfn(). Since dev->dma_mask is always u64
and dev_max_pfn is supposed to be returning the pfn of the dma_mask, it
should unconditionally be 64 bits as well. Either that or it should
return dma_addr_t.
James
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