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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

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@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.

-- 
Ville Syrjälä
Intel OTC