[Mesa-dev] [PATCH 03/10] mesa/st: add endian_format field to struct pipe_resource

[Oded Gabbay]

On Tue, Apr 12, 2016 at 10:21 AM, Michel Dänzer <michel at daenzer.net> wrote:
> On 11.04.2016 23:34, Oded Gabbay wrote:
>> This patch adds a new field, called "endian_format", to
>> "struct pipe_resource". The new field is of type "enum pipe_endian" and
>> can receive one of two values:
>> - PIPE_ENDIAN_LITTLE
>> - PIPE_ENDIAN_NATIVE
>>
>> PIPE_ENDIAN_NATIVE is initialized to either PIPE_ENDIAN_LITTLE or
>> PIPE_ENDIAN_BIG during build time.
>>
>> This field is needed to provide information to the H/W drivers about the
>> endianess current state or desired state of the resource. In other words,
>> for resources that are the source of the operation, this field indicates
>> the resource's current memory layout endianess (big or little endian).
>> For resources that are the destination of the operation, this field
>> indicates the resource's desired memory layout endianess.
>>
>> This field is mandatory because of how mesa works. When we get into the
>> H/W driver functions, the driver *ususally* doesn't know if it is doing a
>> CPU->GPU, a GPU->CPU, a CPU->CPU or a GPU->GPU operation, as this
>> information is "hidden" by the fact we go through common code
>> paths (state tracker layer).
>
> That shouldn't matter if the formats are defined completely and their
> usage is consistent across the board. Sounds like either or both of
> those conditions aren't completely true yet. I agree with Roland that
> this should be addressed fundamentally rather than adding more hacks on top.

I disagree with your statement. The formats are defined correctly,
it's just that the software rendering drivers can use the
automatically generated functions in u_format_table.c to handle all
the endianess issues, while H/W drivers won't do it. So H/W drivers
need additional hint.

In any case, I have no intentions what-so-ever to re-work the entire
mesa/gallium formats system again.

Oded

>
>
> --
> Earthling Michel Dänzer               |               http://www.amd.com
> Libre software enthusiast             |             Mesa and X developer