[PATCH] drm: edid: add support for E-DDC

[Shirish S]

Hello Ville,

On Wed, Aug 22, 2012 at 12:52 AM, Ville Syrjälä <
ville.syrjala at linux.intel.com> wrote:

> On Tue, Aug 21, 2012 at 04:28:20PM -0700, Shirish S wrote:
> > On Tue, Aug 21, 2012 at 7:56 AM, Ville Syrjälä <
> > ville.syrjala at linux.intel.com> wrote:
> >
> > > On Tue, Aug 21, 2012 at 06:55:53AM -0700, Shirish S wrote:
> > Here are my earlier comments on Jean's patch:
> > >
> http://lists.freedesktop.org/archives/dri-devel/2012-February/019069.html
> > >
> > >
> >  If i am not wrong am doing exactly what you have said in you comments.
> >
> > This seems a bit wrong to me. The spec says that the ack for the
> > segment address is "don't care", but for the segment pointer the ack is
> > required (when segment != 0).
> > The variable segFlags is "dont care for block 0 and 1 wheras".
> >
> > With I2C_M_IGNORE_NAK we would in fact end up reading segment 0 from a
> > non E-DDC display, if we try to read segment != 0 from it. Of course
> > we shouldn't do that unless the display lied to us about what extension
> > blocks it provides.
> >
> > So I'm not sure if it would be better to trust that the display never
> > lies about the extension blocks, or if we should just assume all E-DDC
> > displays ack both segment addr and pointer. The no-ack feature seems
> > to there for backwards compatibility, for cases where the host always
> > sends the segment addr/pointer even when reading segment 0 (which your
> > code doesn't do).
> >
> > To handle it exactly as the spec says, I2C_M_IGNORE_NAK should be split
> > into two flags (one for addr, other for data).
> >
> > Hence i have split the i2c_msg into 3, segment pointer,offset(addr)
> > and data pointer.
>
> I was referring to the addr and data phases of the segment pointer.
> According to the spec the ack for the addr is always optional. But I
> suppose no sane device would nak the addr, while acking the data.
>
> Thanks for your comment, actually there was a mistake in my code,
i have posted the second set.
Kindly have a look.

> --
> Ville Syrjälä
> Intel OTC
>
Regards,
Shirish S
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