[PATCH xserver] glamor_egl: request GL2.1 when requesting Desktop GL context

[Eric Anholt]

Icenowy Zheng <icenowy at aosc.io> writes:

> Some devices cannot support OpenGL 2.1, which is the minimum desktop GL
> version required by glamor. However, they may support OpenGL ES 2.0,
> which is the GLES version required by glamor. Usually in this situation
> the desktop GL version supported is 2.0 or 1.4.
>
> Currently, as no requirements are passed when creating desktop GL
> context, a OpenGL 1.4/2.0 context will be created, and glamor will
> arguing that the context is not suitable, although the GPU supports a
> suitable GLES context.
>
> Add version number 2.1 requirement when requesting non-core desktop GL
> context (core context has at least 3.1), so it will fall back to create
> GLES contexts when the version number requirement is not met.
>
> Tested on a Intel 945GMS integrated GPU, which supports GL 1.4 and GLES
> 2.0. Before applying this, it will fail to launch X server when no
> configuration is present because of glamor initialization failure, after
> applying glamor will start with GLES.

In commit:

commit 4218a1e066cf39bb980ebbc9f69536c85232da5c
Author: Olivier Fourdan <ofourdan at redhat.com>
Date:   Thu Feb 5 11:59:22 2015 +0100

    glamor: check max native ALU instructions

a check was introduced on desktop GL to keep i915 from using glamor,
because it just falls back to swrast all the time.  Before enabling
glamor on i915 again after Mesa stopped exposing desktop 2.x on i915
(for similar reasons, but for chromium), we would want to diagnose those
and have some less-slow-paths for glamor on i915.
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