> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Tuesday, July 16, 2013 5:01 PM
> To: Yoder Stuart-B08248
> Cc: Wood Scott-B07421; Alex Williamson; Alexander Graf; Bhushan
> Bharat-R65777; Sethi Varun-B16395;
> virtualizat...@lists.linux-foundation.org; Antonios Motakis;
> k...@vger.kernel.org list; kvm-
> p...@vger.kernel.org; kvm...@lists.cs.columbia.edu
> Subject: Re: RFC: vfio interface for platform devices
>
> On 07/16/2013 04:51:12 PM, Yoder Stuart-B08248 wrote:
> > > > 3. VFIO_DEVICE_GET_REGION_INFO
> > > >
> > > > No changes needed, except perhaps adding a new flag. Freescale
> > > > has some
> > > > devices with regions that must be mapped cacheable.
> > >
> > > While I don't object to making the information available to the user
> > > just in case, the main thing we need here is to influence what the
> > > kernel does when the user tries to map it. At least on PPC it's
> > not up
> > > to userspace to select whether a mmap is cacheable.
> >
> > If user space really can't do anything with the 'cacheable'
> > flag, do you think there is good reason to keep it? Will it
> > help any decision that user space makes? Maybe we should just
> > drop it.
>
> As long as we can be sure all architectures will map things correctly
> without any flags needing to be specified, that's fine.
>
> > > > struct vfio_path_info {
> > > > __u32 argsz;
> > > > __u32 flags;
> > > > #define VFIO_DEVTREE_INFO_RANGES (1 << 3) /* the region
> > is a
> > > > "ranges" property */
> > >
> > > What about distinguishing a normal interrupt from one found in an
> > > interrupt-map?
> >
> > I'm not sure we need that. The kernel needs to use the interrupt
> > map to get interrupts hooked up right, but all user space needs to
> > know is that there are N interrupts and possibly device tree
> > paths to help user space interpret which interrupt is which.
>
> What if the interrupt map is for devices without explicit nodes, such
> as with a PCI controller (ignore the fact that we would normally use
> vfio_pci for the indivdual PCI devices instead)?
>
> You could say the same thing about ranges -- why expose ranges instead
> of the individual child node regs after translation?
Hmm...yes, I guess ranges and interrupt-map fall into the same
basic type of resource category. I'm not sure it's realistic
to pass entire bus controllers through to user space vs
just individual devices on a bus, but I guess it's theoretically
possible.
So the question is whether we future proof by adding flags
for both ranges and interrupt-map, or wait until there is
an actual need for it.
> > > In the case of both ranges and interrupt-maps, we'll also want to
> > > decide what the policy is for when to expose them directly, versus
> > just
> > > using them to translate regs and interrupts of child nodes
> >
> > Yes, not sure the best approach there...but guess we can cross
> > that bridge when we implement this. It doesn't affect this
> > interface.
>
> It does affect the interface, because if you allow either of them to be
> mapped directly (rather than implicitly used when mapping a child
> node), you need a way to indicate which type of resource it is you're
> describing (as you already do for reg/ranges).
>
> It also affects how vfio device binding is done, even if only to the
> point of specifying default behavior in the absence of knobs which
> change whether interrupt maps and/or ranges are mapped.
My opinion is that we want to expose the regs and interrupts for
individual nodes by default, not ranges (or interrupt maps). When someone
needs ranges/interrupt-map in the future they'll need to figure out some
means for the vfio layer to do the right thing. It's complicated
and I would be surprised to see someone need it.
> > > > __u8 path[]; /* output: Full path to associated
> > > > device tree node */
> > >
> > > How does the caller know what size buffer to supply for this?
>
> Ping
This is in the v2 RFC... the caller invokes the ioctl which returns
the complete/full size, then re-allocs the buffer and calls the
ioctl again. Or, as Alex suggested, just use a sufficiently large
buffer to start with.
Stuart
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