[Mesa-dev] Broadcom VC4 project

Roland Scheidegger sroland at vmware.com
Thu Jun 19 10:13:51 PDT 2014

Am 19.06.2014 09:54, schrieb Eric Anholt:
> Dave Airlie <airlied at gmail.com> writes:
>>> I'm working toward building a Mesa driver for Broadcom VC4 (aka
>>> Raspberry Pi).  At the moment I'm still bringing up the DRM side of
>>> things, but I hope to be doing bits of userspace in the next few days.
>>> Current status is I have a skeleton DRM KMS driver that's going to talk
>>> to the firmware for modesetting, and now I'm starting on the execution
>>> side of things.
>>> I'm probably going to start out doing a gallium driver for simplicity,
>>> to avoid having to do all the DRI crap we've got in brw_context.c and
>>> texture miptree validation and getting user data into VBOs and all that
>>> other almost-boilerplate.  Long term I may end up switching to classic
>>> so I can get swrast fallbacks and the ability to implement single-copy
>>> manually-tiled TexImage uploads like.  For now I want to get to drawing
>>> triangles as soon as I can.
>> Do we know anywhere swrast fallbacks make sense? like except for
>> conformance testing,
>> You've got an armv6 swrast fallbacks are going to be punishing, I
>> don't even think it has neon extensions.
> Yeah, but fallbacks are less punishing than "my screen is black, what's
> going on?!?!" bug reports.

I respectfully disagree. You trade "my screen is black" bug reports
(though more than likely just portions of it will be garbage, at least
with shader capable hw you should never need to fallback for relatively
simple stuff) for "why does my screen only refresh once every 10
seconds" bug reports. In severity from an end user perspective, they are
just as bad.
Besides, the full swrast fallbacks rarely work in a fully "correct"
manner (though it may be permitted by GL invariance rules at least in
some cases) due to differences in rasterization.


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