Re: [PATCH] drm/i915: Support 64b relocations

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, May 01, 2014 at 09:04:50AM +0100, Chris Wilson wrote:
> On Mon, Apr 28, 2014 at 05:18:28PM -0700, Ben Widawsky wrote:
> > All the rest of the code to enable this is in my branch. Without my
> > branch, hitting > 32b offsets is impossible. The code has always
> > "supported" 64b, but it's never actually been run of tested. This change
> > doesn't actually fix anything. [1] I am not sure why X won't work yet. I
> > do not get hangs or obvious errors.
> > 
> > There are 3 fixes grouped together here. First is to remove the
> > hardcoded 0 for the upper dword of the relocation. The next fix is to
> > use a 64b value for target_offset. The final fix is to not directly
> > apply target_offset to reloc->delta. reloc->delta is part of ABI, and so
> > we cannot change it. As it stands, 32b is enough to represent everything
> > we're interested in representing anyway. The main problem is, we cannot
> > add greater than 32b values to it directly.

Imo if you have a target_offset > 32b in a valid use-case we can bother to
look at this. But not before, since I expect that hw advances will make
this obsolete anyway.

> > [1] Almost all of intel-gpu-tools is not yet ready to test 64b
> > relocations. There are a few places that expect 32b values for offsets
> > and these all won't work.
> > 
> > Cc: Rafael Barbalho <rafael.barbalho@intel.com>
> > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> 
> Seriously, we did this? I am ashamed. I was annoyed by the original
> assertion that no userspace was ready in the first place, and to see
> that the code was a complete farce anyway...

Well my idea was that we try to prep userspace to avoid a needless abi
rev, but it was always clear to me that the kernel side (and igt) is
hopelessly broken for 64b relocs.

> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

Queued for -next, thanks for the patch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch