linux-kernel - Re: ISP1760 driver crashes

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Message-ID: <20081119172125.GS26308@kernel.dk>
Date:	Wed, 19 Nov 2008 18:21:25 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	"Hommel, Thomas (GE EntSol, Intelligent Platforms)" 
	<Thomas.Hommel@...anuc.com>, USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	James.Bottomley@...senPartnership.com
Subject: Re: ISP1760 driver crashes

On Wed, Nov 19 2008, Alan Stern wrote:
> On Wed, 19 Nov 2008, Jens Axboe wrote:
> 
> > > --- usb-2.6.orig/drivers/scsi/scsi_lib.c
> > > +++ usb-2.6/drivers/scsi/scsi_lib.c
> > > @@ -1684,7 +1684,7 @@ static void scsi_request_fn(struct reque
> > >  u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
> > >  {
> > >  	struct device *host_dev;
> > > -	u64 bounce_limit = 0xffffffff;
> > > +	u64 bounce_limit = BLK_BOUNCE_HIGH;
> > >  
> > >  	if (shost->unchecked_isa_dma)
> > >  		return BLK_BOUNCE_ISA;
> > > 
> > 
> > The best solution is probably to either provide a "doesn't do highmem"
> > in the scsi host template, or provide an appropriate DMA mask for the
> > pci device to indicate it through that setting instead.
> 
> The DMA mask is currently set to NULL.  Is that not appropriate for a 
> device that can't do DMA?  If not, then what would be appropriate?

It's changing behaviour. There's no current rule that says if you don't
have a dma mask set, we only do PIO (even if such a rule DOES make
sense). Additionally, you don't HAVE to bounce for PIO. As I wrote
earlier, it's perfectly feasible to use bio kmap'ings to do the
transfer.

> Also, is the patch above not correct?

It'll certainly work in the sense that if you don't have a dma_mask set,
you only get lowmem pages. Whether the new behaviour is something we
want, not sure. Check with James what he thinks, it's his domain.

-- 
Jens Axboe

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