Re: [RFC/RFT PATCH 3/5] scsi: Use dma_max_pfn(dev) helper for bounce_limitcalculations

[Sergei Shtylyov]

Hello.

On 07/13/2013 02:25 AM, Russell King - ARM Linux wrote:

> > > DMA bounce limit is the maximum direct DMA'able memory beyond which
> > > bounce buffers has to be used to perform dma operations. SCSI driver
> > > relies on dma_mask but its calculation is based on max_*pfn which
> > > don't have uniform meaning across architectures. So make use of
> > > dma_max_pfn() which is expected to return the DMAable maximum pfn
> > > value across architectures.

> > > Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> > > Cc: linux-scsi@xxxxxxxxxxxxxxx

> > > Signed-off-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
> > > ---
> > >    drivers/scsi/scsi_lib.c |    2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)

> > > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> > > index 86d5220..e8275fa 100644
> > > --- a/drivers/scsi/scsi_lib.c
> > > +++ b/drivers/scsi/scsi_lib.c
> > > @@ -1668,7 +1668,7 @@ u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
> > >
> > >    	host_dev = scsi_get_device(shost);
> > >    	if (host_dev && host_dev->dma_mask)
> > > -		bounce_limit = *host_dev->dma_mask;
> > > +		bounce_limit = dma_max_pfn(host_dev) << PAGE_SHIFT;

> >     You definitely forgot -1 here.

> Please explain your point.

   Previously, 'bounce_limit' would look like 0xffffffff (unless I'm 
mistaken), now it would look like 0xfffff000 which is hardly what we're 
looking for, no?

WBR, Sergei

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/