Re: [PATCH] mesa: potentially enable texture float for gallium

[Trevor Woerner <twoerner@gmail.com>]

On Tue 2017-05-30 @ 08:47:55 AM, Richard Purdie wrote:
> We should look at how Fedora "just bars float on llvmpipe and softpipe"
> and perhaps look at copying that? Not that we enable llvmpipe at the
> moment either mind so presumably we're using softpipe.

If you build for AMD's gizmo2 (meta-amd), it uses llvmpipe (although it's
doing a lot of its own stuff with mesa):

	http://git.yoctoproject.org/cgit/cgit.cgi/meta-amd/tree/common/recipes-graphics/mesa/mesa_git.bbappend?h=master


Here is the relevant part of Fedora's mesa.spec file for Fedora 25 (with line
numbers):

	 400 %configure \
	 401     %{?asm_flags} \
	 402     --enable-libglvnd \
	 403     --enable-selinux \
	 404     --enable-gallium-osmesa \
	 405     --with-dri-driverdir=%{_libdir}/dri \
	 406     --enable-egl \
	 407     --disable-gles1 \
	 408     --enable-gles2 \
	 409     --disable-xvmc \
	 410     %{?with_vdpau:--enable-vdpau} \
	 411     %{?with_vaapi:--enable-va} \
	 412     --with-egl-platforms=x11,drm,surfaceless%{?with_wayland:,wayland} \
	 413     --enable-shared-glapi \
	 414     --enable-gbm \
	 415     %{?with_omx:--enable-omx} \
	 416     %{?with_opencl:--enable-opencl --enable-opencl-icd} %{!?with_opencl:--disable-opencl} \
	 417     --enable-glx-tls \
	 418     --enable-texture-float=yes \
	 419 %if %{with_vulkan}
	 420     %{?vulkan_drivers} \
	 421 %endif
	 422     %{?with_llvm:--enable-gallium-llvm} \
	 423     %{?with_llvm:--enable-llvm-shared-libs} \
	 424     --enable-dri \
	 425 %if %{with_hardware}
	 426     %{?with_xa:--enable-xa} \
	 427     %{?with_nine:--enable-nine} \
	 428     --with-gallium-drivers=%{?with_vmware:svga,}%{?with_radeonsi:radeonsi,}%{?with_llvm:swrast,r600,}%{?with_freedreno:freedreno,}%{?with_etnaviv:etnaviv,}%{?with_vc4:vc4,}%{?with_ilo:ilo,}virgl,r300,nouveau \
	 429 %else
	 430     --with-gallium-drivers=%{?with_llvm:swrast,}virgl \
	 431 %endif
	 432     %{?dri_drivers}

--enable-texture-float (line 418) is always, unconditionally enabled. However,
mesa itself is then patched (for Fedora) so that the --enable-texture-float
configuration option doesn't have any effect on llvm and swrast. I.e. it is
easier to do this optional check in code than on the ./configure line:

	From 00bcd599310dc7fce4fe336ffd85902429051a0c Mon Sep 17 00:00:00 2001
	From: Igor Gnatenko <i.gnatenko.brain@gmail.com>
	Date: Sun, 20 Mar 2016 13:27:04 +0100
	Subject: [PATCH 2/4] hardware gloat

	Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>
	---
	 src/gallium/drivers/llvmpipe/lp_screen.c | 7 +++++++
	 src/gallium/drivers/softpipe/sp_screen.c | 7 +++++++
	 2 files changed, 14 insertions(+)

	diff --git a/src/gallium/drivers/llvmpipe/lp_screen.c b/src/gallium/drivers/llvmpipe/lp_screen.c
	index 4f61de8..3b0ec77 100644
	--- a/src/gallium/drivers/llvmpipe/lp_screen.c
	+++ b/src/gallium/drivers/llvmpipe/lp_screen.c
	@@ -411,6 +411,13 @@ llvmpipe_is_format_supported( struct pipe_screen *_screen,
	    if (!format_desc)
	       return FALSE;
	 
	+   if ((bind & PIPE_BIND_RENDER_TARGET) &&
	+       format != PIPE_FORMAT_R9G9B9E5_FLOAT &&
	+       format != PIPE_FORMAT_R11G11B10_FLOAT &&
	+       util_format_is_float(format)) {
	+      return FALSE;
	+   }
	+
	    assert(target == PIPE_BUFFER ||
		   target == PIPE_TEXTURE_1D ||
		   target == PIPE_TEXTURE_1D_ARRAY ||
	diff --git a/src/gallium/drivers/softpipe/sp_screen.c b/src/gallium/drivers/softpipe/sp_screen.c
	index 031602b..c279120 100644
	--- a/src/gallium/drivers/softpipe/sp_screen.c
	+++ b/src/gallium/drivers/softpipe/sp_screen.c
	@@ -358,6 +358,13 @@ softpipe_is_format_supported( struct pipe_screen *screen,
	    if (!format_desc)
	       return FALSE;
	 
	+   if ((bind & PIPE_BIND_RENDER_TARGET) &&
	+       format != PIPE_FORMAT_R9G9B9E5_FLOAT &&
	+       format != PIPE_FORMAT_R11G11B10_FLOAT &&
	+       util_format_is_float(format)) {
	+      return FALSE;
	+   }
	+
	    if (sample_count > 1)
	       return FALSE;
	 
	-- 
	2.7.4


Maybe this would be a better way forward? Enable it, always, in ./configure,
add the patch to check for it in the code itself, then you can build for all
the gallium targets (including swrast) and know that the patented code will
only kick in where it's supported in hardware (and thus patent-safe)?