On Tue, 2007-10-02 at 10:05 -0500, James Bottomley wrote:
> On Tue, 2007-10-02 at 17:02 +0200, Kay Sievers wrote:
> > On 10/2/07, James Bottomley <James.Bottomley@xxxxxxxxxxxx> wrote:
> > > On Mon, 2007-10-01 at 21:22 -0700, Greg KH wrote:
> > > > On Mon, Oct 01, 2007 at 07:39:02PM -0600, Matthew Wilcox wrote:
> > > > > On Mon, Oct 01, 2007 at 07:36:10PM -0400, James Bottomley wrote:
> > > > > > One possibility we could do is to add a
> > > > > >
> > > > > > struct dma_device {
> > > > > > struct device dev;
> > > > > > u64 dma_mask;
> > > > > > u64 coherent_dma_mask;
> > > > > > unsigned int max_segment_size;
> > > > > > /* plus any other DMA parameters */
> > > > > > };
> > > > > >
> > > > > > but then every bus that can do DMA would need to include a struct
> > > > > > dma_device instead of the struct device they do now. Then the IOMMU
> > > > > > would know it could cast out from struct device to struct dma_device,
> > > > > > but this would be a lot of work to thread through the current
> > > > > > infrastructure.
> > > >
> > > > Why not just hang these fields off of a struct device, that way if the
> > > > device doesn't/can't do dma, it only has the "loss" of a single pointer,
> > > > not all of these fields?
> > >
> > > Well, that's just a bit ugly ... I assume you're thinking of adding a
> > > struct device_dma_parameters, and then defining the platform device as
> > >
> > > struct pci_dev {
> > > ...
> > > struct device dev;
> > > struct device_dma_parameters dma_parms;
> > > ...
> > > };
> > >
> > > and then setting up the pointer?
> >
> > I guess Greg means:
> > struct device {
> > ...
> > struct device_dma_parameters *dma_parms;
> > }
> >
> > and allocate dma_parms on demand.
>
> But they're demanded by every bus (with the possible exception of
> PCMCIA) because they'll be holding the dma mask. Sure, we could do a
> separate allocation in every bus device creation routine, but isn't that
> even more complex than sticking them in the global allocation of the bus
> device because the failure modes are now more complex?
Hmm, SCSI devices are bus devices too, will they need it?
Kay
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