On 09/05/16 23:57, Laurent Pinchart wrote:
>> fwiw, I guess a lot of data from that table could these days be
>> replaced w/ some of the drm format helpers
>> (drm_format_num_planes()/drm_format_plane_cpp()/drm_format_{horz,vert}_chrom
>> a_subsampling()/etc)
>
> I don't like those helpers as they're inefficient. Drivers often need to know
> multiple pieces of information about a format, and the API forces look-ups for
> every piece of information needed.
>
> Would it make sense to add a drm_format_info() function that returns a pointer
> to a data structure that describes the format, and reimplement the existing
> helpers on top of that ?
I do like that idea.
A table implementation might possibly be faster even with the current
API. Those big switch-cases compile into a big pile of
if-else-if-else-ifs, whereas a for loop would compile into just a few
instructions. But just guessing here =).
In theory, the table could be sorted, making the lookup much faster, but
I'm not sure if that's worth the effort.
Tomi
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