[PATCH] Fix uses of dma_max_pfn() when converting to a limiting address

[Santosh Shilimkar]

On Tuesday 11 February 2014 12:28 PM, 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 at arm.linux.org.uk>
> ---
> 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
>
You are right. We were seeing an issue with SCSI HDD over PCI and
the patch fixes that issue as well.

I think we should send this patch to stable as well. At least 3.13
should get this patch.

Thanks RMK for the bug fix. Feel free to add, in case the patch is
not committed already

Tested-Acked-by: Santosh Shilimkar <santosh.shilimkar at ti.com>
 
>  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;
>  
>  	return bounce_limit;
>  }
>