Re: [PATCH v2 16/37] drm/i915/lmem: support pread

Daniel Vetter
2019-07-30T09:50:42Z

On Tue, Jul 30, 2019 at 10:25:10AM +0100, Matthew Auld wrote:
> On 30/07/2019 09:58, Daniel Vetter wrote:
> > On Thu, Jun 27, 2019 at 09:56:12PM +0100, Matthew Auld wrote:
> > > We need to add support for pread'ing an LMEM object.
> >
> > Why? Usage outside from igts seems pretty dead, at least looking at iris
> > and anv. This was kinda a neat thing for when we didn't yet realized that
> > doing clflush in userspace is both possible and more efficient.
> >
> > Same for pwrite, iris just dropped it, anv doesn't seem to use it. And I
> > thought mesa plan is to drop the old classic driver for when we'll need
> > lmem. It's not much, but would allow us to drop a few things.
>
> Hmm, it was at least useful in the super early days for debugging. If we
> were to drop this what do we do with the igts? Just use mmap?

wc mmap is probably simplest. I think we could do a compat function in igt
that does that when pwrite isn't available. Could also have that in
libdrm_intel, in case some of the UMDs have a hard time getting off it.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation