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[212.51.149.96]) by smtp.gmail.com with ESMTPSA id u27sm395824edb.48.2019.10.09.08.10.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Oct 2019 08:10:43 -0700 (PDT) Date: Wed, 9 Oct 2019 17:10:24 +0200 From: Daniel Vetter To: Ilia Mirkin Cc: Brian Starkey , nd , "Oscar Zhang (Arm Technology China)" , "Tiannan Zhu (Arm Technology China)" , Mihail Atanassov , "airlied@linux.ie" , "Jonathan Chai (Arm Technology China)" , Liviu Dudau , "linux-kernel@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "Julien Yin (Arm Technology China)" , "Channing Chen (Arm Technology China)" , "james qian wang (Arm Technology China)" , "Yiqi Kang (Arm Technology China)" , Ben Davis , "Thomas Sun (Arm Technology China)" , Ayan Halder , "sean@poorly.run" , "Lowry Li (Arm Technology China)" Subject: Re: [PATCH 2/3] drm/komeda: Add drm_ctm_to_coeffs() Message-ID: <20191009151024.GF16989@phenom.ffwll.local> Mail-Followup-To: Ilia Mirkin , Brian Starkey , nd , "Oscar Zhang (Arm Technology China)" , "Tiannan Zhu (Arm Technology China)" , Mihail Atanassov , "airlied@linux.ie" , "Jonathan Chai (Arm Technology China)" , Liviu Dudau , "linux-kernel@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "Julien Yin (Arm Technology China)" , "Channing Chen (Arm Technology China)" , "james qian wang (Arm Technology China)" , "Yiqi Kang (Arm Technology China)" , Ben Davis , "Thomas Sun (Arm Technology China)" , Ayan Halder , "sean@poorly.run" , "Lowry Li (Arm Technology China)" References: <20190930045408.8053-1-james.qian.wang@arm.com> <20190930045408.8053-3-james.qian.wang@arm.com> <20190930110438.6w7jtw2e5s2ykwnd@DESKTOP-E1NTVVP.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: Linux phenom 5.2.0-2-amd64 User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 30, 2019 at 07:56:13AM -0400, Ilia Mirkin wrote: > On Mon, Sep 30, 2019 at 7:05 AM Brian Starkey wrote: > > > > Hi James, > > > > On Mon, Sep 30, 2019 at 04:54:41AM +0000, james qian wang (Arm Technology China) wrote: > > > This function is used to convert drm_color_ctm S31.32 sign-magnitude > > > value to komeda required Q2.12 2's complement > > > > > > Signed-off-by: james qian wang (Arm Technology China) > > > --- > > > .../arm/display/komeda/komeda_color_mgmt.c | 27 +++++++++++++++++++ > > > .../arm/display/komeda/komeda_color_mgmt.h | 1 + > > > 2 files changed, 28 insertions(+) > > > > > > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c b/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c > > > index c180ce70c26c..c92c82eebddb 100644 > > > --- a/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c > > > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_color_mgmt.c > > > @@ -117,3 +117,30 @@ void drm_lut_to_fgamma_coeffs(struct drm_property_blob *lut_blob, u32 *coeffs) > > > { > > > drm_lut_to_coeffs(lut_blob, coeffs, sector_tbl, ARRAY_SIZE(sector_tbl)); > > > } > > > + > > > +/* Convert from S31.32 sign-magnitude to HW Q2.12 2's complement */ > > > +static s32 drm_ctm_s31_32_to_q2_12(u64 input) > > > +{ > > > + u64 mag = (input & ~BIT_ULL(63)) >> 20; > > > + bool negative = !!(input & BIT_ULL(63)); > > > + u32 val; > > > + > > > + /* the range of signed 2s complement is [-2^n, 2^n - 1] */ > > > + val = clamp_val(mag, 0, negative ? BIT(14) : BIT(14) - 1); > > > + > > > + return negative ? 0 - val : val; > > > +} > > > > This function looks generally useful. Should it be in DRM core > > (assuming there isn't already one there)? > > > > You can use a parameter to determine the number of bits desired in the > > output. > > I suspect every driver needs to do something similar. You can see what > I did for nouveau here: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=88b703527ba70659365d989f29579f1292ebf9c3 > > (look for csc_drm_to_base) > > Would be great to have a common helper which correctly accounts for > all the variability. Yeah the sign-bit 31.32 fixed point format is probably the most ludicrous uapi fumble we've ever done. A shared function, rolled out to drivers, to switch it to a signed 2 complements integer sounds like a _very_ good idea. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch