Re: [PATCH v2 1/4] drm/komeda: Add a new helper drm_color_ctm_s31_32_to_qm_n()

[james qian wang (Arm Technology China)]

On Mon, Oct 14, 2019 at 10:56:05AM +0200, Daniel Vetter wrote:
> On Fri, Oct 11, 2019 at 05:43:09AM +0000, james qian wang (Arm Technology China) wrote:
> > Add a new helper function drm_color_ctm_s31_32_to_qm_n() for driver to
> > convert S31.32 sign-magnitude to Qm.n 2's complement that supported by
> > hardware.
> >
> > Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@xxxxxxx>
> > ---
> >  drivers/gpu/drm/drm_color_mgmt.c | 23 +++++++++++++++++++++++
> >  include/drm/drm_color_mgmt.h     |  2 ++
> >  2 files changed, 25 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
> > index 4ce5c6d8de99..3d533d0b45af 100644
> > --- a/drivers/gpu/drm/drm_color_mgmt.c
> > +++ b/drivers/gpu/drm/drm_color_mgmt.c
> > @@ -132,6 +132,29 @@ uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision)
> >  }
> >  EXPORT_SYMBOL(drm_color_lut_extract);
> >
> > +/**
> > + * drm_color_ctm_s31_32_to_qm_n
> > + *
> > + * @user_input: input value
> > + * @m: number of integer bits
> > + * @n: number of fractinal bits
> > + *
> > + * Convert and clamp S31.32 sign-magnitude to Qm.n 2's complement.
>
> What's the Q meaning here? Also maybe specify that the higher bits above
> m+n are cleared to all 0 or all 1. Unit test would be lovely too. Anyway:

The Q used to represent signed two's complement.

For detail: https://en.wikipedia.org/wiki/Q_(number_format)

And it Q is 2's complement, so the value of higher bit equal to
sign-bit.
All 1 if it is negative
0 if it is positive.

James

> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
>
> > + */
> > +uint64_t drm_color_ctm_s31_32_to_qm_n(uint64_t user_input,
> > +                                 uint32_t m, uint32_t n)
> > +{
> > +   u64 mag = (user_input & ~BIT_ULL(63)) >> (32 - n);
> > +   bool negative = !!(user_input & BIT_ULL(63));
> > +   s64 val;
> > +
> > +   /* the range of signed 2s complement is [-2^n+m, 2^n+m - 1] */
> > +   val = clamp_val(mag, 0, negative ? BIT(n + m) : BIT(n + m) - 1);
> > +
> > +   return negative ? 0ll - val : val;
> > +}
> > +EXPORT_SYMBOL(drm_color_ctm_s31_32_to_qm_n);
> > +
> >  /**
> >   * drm_crtc_enable_color_mgmt - enable color management properties
> >   * @crtc: DRM CRTC
> > diff --git a/include/drm/drm_color_mgmt.h b/include/drm/drm_color_mgmt.h
> > index d1c662d92ab7..60fea5501886 100644
> > --- a/include/drm/drm_color_mgmt.h
> > +++ b/include/drm/drm_color_mgmt.h
> > @@ -30,6 +30,8 @@ struct drm_crtc;
> >  struct drm_plane;
> >
> >  uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision);
> > +uint64_t drm_color_ctm_s31_32_to_qm_n(uint64_t user_input,
> > +                                 uint32_t m, uint32_t n);
> >
> >  void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc,
> >                             uint degamma_lut_size,
> > --
> > 2.20.1
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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