On Sun, 2008-11-16 at 23:31 +0100, Andi Kleen wrote:
> On Sun, Nov 16, 2008 at 10:46:16AM -0500, James Bottomley wrote:
> > On Sun, 2008-11-16 at 00:11 +0100, Andi Kleen wrote:
> > > +static struct Scsi_Host *buslogic_host_alloc(gfp_t gfp)
> > > +{
> > > + struct BusLogic_HostAdapter *board;
> > > + struct Scsi_Host *shost;
> > > +
> > > +
> > > + shost = scsi_host_alloc(&Bus_Logic_template, sizeof(struct host_ptr));
> > > + if (!shost)
> > > + return NULL;
> > > +
> > > + board = dma_alloc_coherent(NULL, sizeof(struct BusLogic_HostAdapter),
> > > + &bl_shost_dma(shost), GFP_KERNEL);
> > > + if (!board) {
> > > + scsi_host_put(shost);
> > > + return NULL;
> > > + }
> >
> > What makes you think that BusLogic_HostAdapter has to be in coherent
> > memory? You can tell from your own patch that nothing ever uses its DMA
> > address, so the card never actually DMAs data to or from this area.
>
> Hmm I think it was mostly about having an equivalent transformation.
> The structure was in GFP_DMA before, so I wanted to keep that
>
> Also the driver does some funny things with transforming some
> bus addresses on its own, which made me double conservative.
> On looking more closely it doesn't do virt_to_bus, but at least
> one bus_to_virt (but it seems to data outside BusAdapter)
>
> I don't have that hardware so I wanted to be very conservative
> in any
>
> But I'll fix it in the next version.
Yes, the problem is that on several architectures dma_alloc_coherent()
uses a special vaddr to get coherent memory. Unless you use it by the
returned handle (which I've checked the patch doesn't do) the use is
likely invalid. In particular, you can't call dma_map_... on it because
usually that sets up a dual mapping (one cached and one uncached most
likely) which is illegal on most CPUs (even x86, I believe).
James
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