Re: [PATCH 4/5] drm/msm/dpu1: Account for DSC's bits_per_pixel having 4 fractional bits

[Dmitry Baryshkov]

On Sat, 1 Oct 2022 at 22:08, Marijn Suijten
<marijn.suijten@xxxxxxxxxxxxxx> wrote:
>
> According to the comment this DPU register contains the bits per pixel
> as a 6.4 fractional value, conveniently matching the contents of
> bits_per_pixel in struct drm_dsc_config which also uses 4 fractional
> bits.  However, the downstream source this implementation was
> copy-pasted from has its bpp field stored _without_ fractional part.
>
> This makes the entire convoluted math obsolete as it is impossible to
> pull those 4 fractional bits out of thin air, by somehow trying to reuse
> the lowest 2 bits of a non-fractional bpp (lsb = bpp % 4??).
>
> The rest of the code merely attempts to keep the integer part a multiple
> of 4, which is rendered useless thanks to data |= dsc->bits_per_pixel <<
> 12; already filling up those bits anyway (but not on downstream).
>
> Fixes: c110cfd1753e ("drm/msm/disp/dpu1: Add support for DSC")
> Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>

> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)

-- 
With best wishes
Dmitry