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

[James Bottomley]

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 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
> 
>  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