Bug 51600

The following patch
http://cgit.freedesktop.org/mesa/mesa/commit/?id=75f409d75cacf90df2d6f1d718251a5d5cd92f7f

for the following bug

https://bugs.freedesktop.org/show_bug.cgi?id=51328

fixed the problem for gen 6 and above but gen 4 still suffering from this bug.

Cheers
Emam

Yeah, the problem here is that it's trying to blit a Y-tiled buffer (depth or depth/stencil), and the Gen4-5 blitters can't do that.  Paul's "blorp" code for doing blits on the render ring (without the hardware blitter) doesn't exist for Gen4-5.  So we hit _meta_BlitFramebuffer.  Which I think hits swrast.

Paul's blorp code could be backported.  However, it's probably overkill: gen4-5 doesn't have/use HiZ and its crazy W-tiled buffer format, so all that code is unnecessary.  It also doesn't have MSAA.  There's no need for "resolves".  Just blits.  So it's probably possible to write a simpler blit path.  I don't honestly know which would be more work.

(In reply to comment #2)
> Paul's blorp code could be backported.  However, it's probably overkill: gen4-5
> doesn't have/use HiZ and its crazy W-tiled buffer format, so all that code is
> unnecessary.  It also doesn't have MSAA.  There's no need for "resolves".  Just
> blits.  So it's probably possible to write a simpler blit path.  I don't
> honestly know which would be more work.

My intuition is that backporting blorp to gen4-5 would be less work.  Blorp is divided between a hardware-specific part (that sets up the 3D pipeline correctly for the blit) and a hardware-agnostic part (that generates the shader code and sets up the parameters for the blit).  Almost all of the code that's unnecessary for gen4-5 is in the hardware-agnostic part, and that code is already smart enough to skip the stuff that's unnecessary (e.g. the MSAA-specific code is only activated when doing MSAA blits).

So I think that the vast majority of the work involved in backporting blorp to gen4-5 would be to write the code to set up the 3D pipeline, and that would have to be done whether we re-use blorp or not.  Given that, I would vastly prefer to re-use blorp.

Incidentally, Ben Widawsky and I are planning to do some investigation into how difficult it would be to use the media pipeline for blorp rather than the 3D pipeline.  Supposedly, the media pipeline is a lot easier to set up than the 3D pipeline, and has fewer differences between hardware generations.  So if we wind up doing this, backporting blorp to gen4-5 might turn out to be fairly straightforward.

Reassigning to Chris, as he's working on BLORP for pre-Sandybridge.

any new on BLORP for pre-Sandybridge

My meta series should fix this (putting steam on the gm45 now)

is BLORP implemented for GM45?

Fixed by the series ending with:

commit 255bd9c0b83e3cb3914ee5a1386c8d5acdbc046a
Author: Eric Anholt <eric@anholt.net>
Date:   Tue Feb 4 23:57:29 2014 -0800

    meta: Add acceleration for depth glBlitFramebuffer().

great!, confirming fixed