Re: [RFC PATCH] HDMI:Support for EDID parsing in kernel.

[Guennadi Liakhovetski <g.liakhovetski@gmx.de>]

On Thu, 24 Mar 2011, K, Mythri P wrote:

> Hi Jesse,
> 
> On Wed, Mar 23, 2011 at 8:48 PM, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> > On Wed, 23 Mar 2011 18:58:27 +0530
> > "K, Mythri P" <mythripk@ti.com> wrote:
> >
> >> Hi Dave,
> >>
> >> On Wed, Mar 23, 2011 at 6:16 AM, Dave Airlie <airlied@gmail.com> wrote:
> >> > On Wed, Mar 23, 2011 at 3:32 AM, Mythri P K <mythripk@ti.com> wrote:
> >> >> Adding support for common EDID parsing in kernel.
> >> >>
> >> >> EDID - Extended display identification data is a data structure provided by
> >> >> a digital display to describe its capabilities to a video source, This a
> >> >> standard supported by CEA and VESA.
> >> >>
> >> >> There are several custom implementations for parsing EDID in kernel, some
> >> >> of them are present in fbmon.c, drm_edid.c, sh_mobile_hdmi.c, Ideally
> >> >> parsing of EDID should be done in a library, which is agnostic of the
> >> >> framework (V4l2, DRM, FB)  which is using the functionality, just based on
> >> >> the raw EDID pointer with size/segment information.
> >> >>
> >> >> With other RFC's such as the one below, which tries to standardize HDMI API's
> >> >> It would be better to have a common EDID code in one place.It also helps to
> >> >> provide better interoperability with variety of TV/Monitor may be even by
> >> >> listing out quirks which might get missed with several custom implementation
> >> >> of EDID.
> >> >> http://permalink.gmane.org/gmane.linux.drivers.video-input-infrastructure/30401
> >> >>
> >> >> This patch tries to add functions to parse some portion EDID (detailed timing,
> >> >> monitor limits, AV delay information, deep color mode support, Audio and VSDB)
> >> >> If we can align on this library approach i can enhance this library to parse
> >> >> other blocks and probably we could also add quirks from other implementation
> >> >> as well.
> >> >>
> >> >
> >> > If you want to take this approach, you need to start from the DRM EDID parser,
> >> > its the most well tested and I can guarantee its been plugged into more monitors
> >> > than any of the others. There is just no way we would move the DRM parser to a
> >> > library one that isn't derived from it + enhancements, as we'd throw away the
> >> > years of testing and the regression count would be way too high.
> >> >
> >> I had a look at the DRM EDID code, but for quirks it looks pretty much the same.
> >> yes i could take quirks and other DRM tested code and enhance, but
> >> still the code has to do away with struct drm_display_mode
> >> which is very much custom to DRM.
> >
> > If that's the only issue you have, we could easily rename that
> > structure or add conversion funcs to a smaller structure if that's what
> > you need.
> >
> > Dave's point is that we can't ditch the existing code without
> > introducing a lot of risk; it would be better to start a library-ized
> > EDID codebase from the most complete one we have already, i.e. the DRM
> > EDID code.

Does the DRM EDID-parser also process blocks beyond the first one and 
also parses SVD entries similar to what I've recently added to fbdev? Yes, 
we definitely need a common EDID parses, and maybe we'll have to collect 
various pieces from different implementations.

Thanks
Guennadi

> >
> This sounds good. If we can remove the DRM dependent portion to have a
> library-ized EDID code,
> That would be perfect. The main Intention to have a library is,
> Instead of having several different Implementation in kernel, all
> doing the same EDID parsing , if we could have one single
> implementation , it would help in better testing and interoperability.
> 
> > Do you really think the differences between your code and the existing
> > DRM code are irreconcilable?
> >
> On the contrary if there is a library-ized  EDID parsing using the
> drm_edid, and there is any delta / fields( Parsing the video block in
> CEA extension for Short Video Descriptor, Vendor block for AV delay
> /Deep color information etc) that are parsed with the RFC i posted i
> would be happy to add.
> 
> Thanks and regards,
> Mythri.
> > --
> > Jesse Barnes, Intel Open Source Technology Center
> >
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---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/