Re: [PATCH 1/4] drm: add picture aspect ratio flags

From: "Sharma, Shashank" <shashank.sharma@intel.com>
To: Emil Velikov <emil.l.velikov@gmail.com>
Cc: "intel-gfx@lists.freedesktop.org"
	<intel-gfx@lists.freedesktop.org>,
	ML dri-devel <dri-devel@lists.freedesktop.org>,
	"Vetter, Daniel" <daniel.vetter@intel.com>
Subject: Re: [PATCH 1/4] drm: add picture aspect ratio flags
Date: Thu, 4 Aug 2016 18:45:43 +0530	[thread overview]
Message-ID: <00744cc7-fee7-950b-6ae2-1dae1bbf6210@intel.com> (raw)
In-Reply-To: <CACvgo50fU8GjeXvwC6StPdtV3=c=ZhJ7PQ7=dNCw7xJdgUtcyQ@mail.gmail.com>

Regards

Shashank

On 8/4/2016 5:04 PM, Emil Velikov wrote:
> On 4 August 2016 at 11:16, Sharma, Shashank <shashank.sharma@intel.com> wrote:
>> Hello Emil,
>>
>> Thanks for your time.
>>
>> I have got mixed opinion on this.
>>
>> IMHO we should expose them to userspace too, as UI agents like Hardware
>> composer/X/Wayland must know what does these
>>
>> flags means, so that they can display them on the end user screen (like
>> settings menu)
>>
>> But few people even think thats its too complex to be exposed to userspace
>> agents.
>>
> If we want these/such flags passed between kernel and user space one must:
>   - Provide a kernel interface how to do that
>   - Provide a userspace (acked by respective developers/maintainers)
> that the approach is sane and proves useful.
>
> Since the above can take some time, I'd suggest dropping those from
> the UAPI header(s)... for now.
>
> -Emil
Please guide me a bit more on this problem, Emil, Daniel.
The reason why I want to pass this to userspace is, so that, HWC/X/any 
other UI manager, can send a modeset
which is accurate upto aspect ratio.

Please think of this complete scenario:
- HDMI compliance testing is going on, and we need to apply a CEA mode 
(for example, VIC=3, mode - 720x480@60Hz aspect 16:9)
- But HWC doesnt pass the aspect ratio  information, and passed only 
720x480@60Hz
- Kernel gets the first matching mode, from edid_cea_modes, which is 
VIC=2 720x480@60Hz (aspect 4:3)
- Kernel does the modeset of VIC = 2, and AVI IF contain VIC=2
- Compliance equipment expects VIC = 3, so fails the test case.

In this case, its essential that the userspace, which is triggering the 
modeset, must know about the aspect ratio field too.
So does this make it a reason to pass this information to usp ?

Regards
Shashank
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