Re: [PATCH v2 04/10] drm: Add Gamma correction structure

From: Emil Velikov <emil.l.velikov@gmail.com>
To: "Jindal, Sonika" <sonika.jindal@intel.com>
Cc: annie.j.matheson@intel.com,
	ML dri-devel <dri-devel@lists.freedesktop.org>,
	vijay.a.purushothaman@intel.com, jesse.barnes@intel.com, "Vetter,
	Daniel" <daniel.vetter@intel.com>,
	dhanya.p.r@intel.com,
	"intel-gfx@lists.freedesktop.org"
	<intel-gfx@lists.freedesktop.org>
Subject: Re: [PATCH v2 04/10] drm: Add Gamma correction structure
Date: Fri, 12 Jun 2015 18:17:47 +0100	[thread overview]
Message-ID: <CACvgo51TyW9aofL8H3y7gBEZMdZKdQu9b+=Rw8bKQ=4ZvUVdNA@mail.gmail.com> (raw)
In-Reply-To: <55718F74.2050407@intel.com>

Hi Kausal Malladi,

On 5 June 2015 at 13:00, Jindal, Sonika <sonika.jindal@intel.com> wrote:
> On 6/4/2015 7:12 PM, Kausal Malladi wrote:
>>
>> From: Kausal Malladi <Kausal.Malladi@intel.com>
>>
...
>> v2: Addressing Daniel Stone's comment, added a variable sized array to
>> carry Gamma correction values as blob property.
>>
>> Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
>> Signed-off-by: Kausal Malladi <Kausal.Malladi@intel.com>
>> ---
>>   include/drm/drm_crtc.h |  3 +++
>>   include/uapi/drm/drm.h | 10 ++++++++++
>>   2 files changed, 13 insertions(+)
>>
...
>> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
>> index 3801584..fc2661c 100644
>> --- a/include/uapi/drm/drm.h
>> +++ b/include/uapi/drm/drm.h
>> @@ -829,6 +829,16 @@ struct drm_event_vblank {
>>         __u32 reserved;
>>   };
>>
>> +/* Color Management structure for Gamma */
>> +struct drm_gamma {
>> +       __u32 flags;
>> +       __u32 gamma_level;
>> +       __u32 gamma_precision;
>> +       __u32 num_samples;
>> +       __u32 reserved;
>> +       __u16 values[0];
Silly question:
Why use zero sized array ? Afaik it's a construct not covered in
C90/C99, which makes sizeof(struct drm_gamma) act funny. There seems
to be no other instance of a zero-sized array in drm uapi, plus based
of Daniel Vettel's "Botching up IOCTLS" I think that using it here
might be a bad idea.

The commit message mentions that Daniel Stone suggested it, but that
email never made it to the dri-devel mailiing list (and many other
emails, as mentioned previously) :'-(

Thanks
Emil
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