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Date:   Mon, 14 Oct 2019 17:33:27 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     "james qian wang (Arm Technology China)" <james.qian.wang@arm.com>
Cc:     Liviu Dudau <Liviu.Dudau@arm.com>,
        "airlied@linux.ie" <airlied@linux.ie>,
        Brian Starkey <Brian.Starkey@arm.com>,
        "maarten.lankhorst@linux.intel.com" 
        <maarten.lankhorst@linux.intel.com>,
        "sean@poorly.run" <sean@poorly.run>,
        "imirkin@alum.mit.edu" <imirkin@alum.mit.edu>, nd <nd@arm.com>,
        Ayan Halder <Ayan.Halder@arm.com>,
        "Oscar Zhang (Arm Technology China)" <Oscar.Zhang@arm.com>,
        "Tiannan Zhu (Arm Technology China)" <Tiannan.Zhu@arm.com>,
        Mihail Atanassov <Mihail.Atanassov@arm.com>,
        "Jonathan Chai (Arm Technology China)" <Jonathan.Chai@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "Julien Yin (Arm Technology China)" <Julien.Yin@arm.com>,
        "Channing Chen (Arm Technology China)" <Channing.Chen@arm.com>,
        "Yiqi Kang (Arm Technology China)" <Yiqi.Kang@arm.com>,
        "Thomas Sun (Arm Technology China)" <thomas.Sun@arm.com>,
        "Lowry Li (Arm Technology China)" <Lowry.Li@arm.com>,
        Ben Davis <Ben.Davis@arm.com>
Subject: Re: [PATCH v2 1/4] drm/komeda: Add a new helper
 drm_color_ctm_s31_32_to_qm_n()
Message-ID: <20191014153327.GL11828@phenom.ffwll.local>
Mail-Followup-To: "james qian wang (Arm Technology China)" <james.qian.wang@arm.com>,
        Liviu Dudau <Liviu.Dudau@arm.com>,
        "airlied@linux.ie" <airlied@linux.ie>,
        Brian Starkey <Brian.Starkey@arm.com>,
        "maarten.lankhorst@linux.intel.com" <maarten.lankhorst@linux.intel.com>,
        "sean@poorly.run" <sean@poorly.run>,
        "imirkin@alum.mit.edu" <imirkin@alum.mit.edu>, nd <nd@arm.com>,
        Ayan Halder <Ayan.Halder@arm.com>,
        "Oscar Zhang (Arm Technology China)" <Oscar.Zhang@arm.com>,
        "Tiannan Zhu (Arm Technology China)" <Tiannan.Zhu@arm.com>,
        Mihail Atanassov <Mihail.Atanassov@arm.com>,
        "Jonathan Chai (Arm Technology China)" <Jonathan.Chai@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "Julien Yin (Arm Technology China)" <Julien.Yin@arm.com>,
        "Channing Chen (Arm Technology China)" <Channing.Chen@arm.com>,
        "Yiqi Kang (Arm Technology China)" <Yiqi.Kang@arm.com>,
        "Thomas Sun (Arm Technology China)" <thomas.Sun@arm.com>,
        "Lowry Li (Arm Technology China)" <Lowry.Li@arm.com>,
        Ben Davis <Ben.Davis@arm.com>
References: <20191011054240.17782-1-james.qian.wang@arm.com>
 <20191011054240.17782-2-james.qian.wang@arm.com>
 <20191014085605.GF11828@phenom.ffwll.local>
 <20191014095813.GA15227@jamwan02-TSP300>
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On Mon, Oct 14, 2019 at 09:58:20AM +0000, james qian wang (Arm Technology China) wrote:
> 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@arm.com>
> > > ---
> > >  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.

Ah I didn't know about this notation, I think in other drm docs we just
used m.n 2's complement to denote this layout. Up to you I think.
-Daniel

> 
> James
> 
> > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> >
> > > + */
> > > +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@lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch