[Mesa-dev] [PATCH 05/17] gallium: reserve one shader buffer for shared storage

[Samuel Pitoiset]

On 01/26/2016 11:36 AM, Marek Olšák wrote:
> I don't understand this. Can you explain it?

This shader buffer for shared storage is actually a fake buffer. Only 
one shared "fake" buffer can be used and it will contain all shared 
variables which are defined in the compute shaders. Its size is defined 
by MAX_COMPUTE_SHARED_MEMORY_SIZE fyi.

I did this change to reserve the slot 32 for it and so it won't be 
allocated by the underlying driver since I clamp the maximum number of 
usable shader+atomic buffers to 32.

>
> AFAIK, shared variables don't need a backing buffer.
>
> Thanks,
> Marek
>
> On Sun, Jan 24, 2016 at 10:09 PM, Samuel Pitoiset
> <samuel.pitoiset at gmail.com> wrote:
>> At least, one shader buffer must be available for compute shaders.
>>
>> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
>> ---
>>   src/gallium/include/pipe/p_state.h     | 2 +-
>>   src/mesa/state_tracker/st_extensions.c | 6 ++++--
>>   2 files changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/src/gallium/include/pipe/p_state.h b/src/gallium/include/pipe/p_state.h
>> index 2e4d283..051856e 100644
>> --- a/src/gallium/include/pipe/p_state.h
>> +++ b/src/gallium/include/pipe/p_state.h
>> @@ -61,7 +61,7 @@ extern "C" {
>>   #define PIPE_MAX_SHADER_INPUTS    80 /* 32 GENERIC + 32 PATCH + 16 others */
>>   #define PIPE_MAX_SHADER_OUTPUTS   80 /* 32 GENERIC + 32 PATCH + 16 others */
>>   #define PIPE_MAX_SHADER_SAMPLER_VIEWS 32
>> -#define PIPE_MAX_SHADER_BUFFERS   32
>> +#define PIPE_MAX_SHADER_BUFFERS   33
>>   #define PIPE_MAX_SHADER_IMAGES    32
>>   #define PIPE_MAX_TEXTURE_LEVELS   16
>>   #define PIPE_MAX_SO_BUFFERS        4
>> diff --git a/src/mesa/state_tracker/st_extensions.c b/src/mesa/state_tracker/st_extensions.c
>> index d066784..c198892 100644
>> --- a/src/mesa/state_tracker/st_extensions.c
>> +++ b/src/mesa/state_tracker/st_extensions.c
>> @@ -219,8 +219,10 @@ void st_init_limits(struct pipe_screen *screen,
>>                                             pc->MaxUniformBlocks);
>>
>>         pc->MaxAtomicCounters = MAX_ATOMIC_COUNTERS;
>> -      pc->MaxAtomicBuffers = screen->get_shader_param(
>> -            screen, sh, PIPE_SHADER_CAP_MAX_SHADER_BUFFERS) / 2;
>> +      pc->MaxAtomicBuffers =
>> +         _clamp(screen->get_shader_param(screen, sh,
>> +                                         PIPE_SHADER_CAP_MAX_SHADER_BUFFERS),
>> +                0, PIPE_MAX_SHADER_BUFFERS - 1) / 2;
>>         pc->MaxShaderStorageBlocks = pc->MaxAtomicBuffers;
>>
>>         /* Gallium doesn't really care about local vs. env parameters so use the
>> --
>> 2.6.4
>>
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-- 
-Samuel