Re: [PATCH 1/5] drm: Add drm_fixed_16_16 helper

On Wed, Sep 01, 2021 at 09:35:40PM -0400, Alyssa Rosenzweig wrote:

quoted

Missing documentation :-)

Ack.

quoted

quoted

+static inline int drm_fixed_16_16(s32 mult, s32 div)

You should return a s32.

Ack.

quoted

The function name isn't very explicit, and departs from the naming
scheme of other functions in the same file. As fixed-point numbers are
stored in a s64 for the drm_fixp_* helpers, we shouldn't rese the
drm_fixp_ prefix, maybe drm_fixp_s16_16_ would be a good prefix. The
function should probably be named drm_fixp_s16_16 from_fraction() then,
but then the same logic should possibly be replicated to ensure optimal
precision. I wonder if it wouldn't be best to simply use
drm_fixp_from_fraction() and shift the result right by 16 bits.

Sure, I'm not attached to the naming ... will wait to hear what colours
everyone else wants the bikehed painted.

As for the implementation, I just went with what was used across
multiple drivers already (no chance of regressions that way) but could
reuse other helpers if it's better..? If the behaviour changes this goes
from a trivial cleanup to a much more invasive changeset. I don't own
half of the hardware here.

But except for msm which may need testing, all other drivers use the
existing FRAC_16_16() macro with constant arguments, so it shouldn't be
difficult to ensure that the new function gives the same results.

-- 
Regards,

Laurent Pinchart

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel