[PATCH V4] drm: edid: add support for E-DDC

[Shirish S]

Hi Jean,

On Wed, Aug 29, 2012 at 6:44 AM, Jean Delvare <jdelvare at suse.de> wrote:

> Hi all,
>
> Sorry for breaking message threading but I was not included in
> iterations 3 and 4 of this patch.
>
> Random comments about v4:
>
> > --- a/drivers/gpu/drm/drm_edid.c
> > +++ b/drivers/gpu/drm/drm_edid.c
> > @@ -254,6 +254,8 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter,
> unsigned
> > char *buf,
> >                       int block, int len)
> >  {
> >         unsigned char start = block * EDID_LENGTH;
> > +       unsigned char segment = block >> 1;
> > +       unsigned char xfers = segment ? 3 : 2;
> >         int ret, retries = 5;
> >
> >         /* The core i2c driver will automatically retry the transfer if
> the
> > @@ -264,7 +266,12 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter,
> > unsigned char *buf,
> >          */
> >         do {
> >                 struct i2c_msg msgs[] = {
> > -                       {
> > +                       { /*set segment pointer */
> > +                               .addr   = DDC_SEGMENT_ADDR,
> > +                               .flags  = segment ? 0 : I2C_M_IGNORE_NAK,
>
> I don't get the idea. If segment == 0, this message is never sent, so the
> value of field flags doesn't matter. So flags will always be 0 when this
> message is sent, so it can be hard-coded.
>
> Agreed.

> But from previous discussions my understanding was an agreement on always
> using I2C_M_IGNORE_NAK for improved compatibility. So I2C_M_IGNORE_NAK
> should be hard-coded, not 0?
>
After discussion,daniel had asked for a seprate patch for the flags
modification.
Will upload that later.

>
>
> +                               .len    = 1,
> > +                               .buf    = &segment,
> > +                       }, {
> >                                 .addr   = DDC_ADDR,
> >                                 .flags  = 0,
> >                                 .len    = 1,
> > @@ -276,15 +283,22 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter,
> > unsigned char *buf,
> >                                 .buf    = buf,
> >                         }
> >                 };
> > -               ret = i2c_transfer(adapter, msgs, 2);
> > +       /* Avoid sending the segment addr to not upset non-compliant ddc
> > +        * monitors.
> > +        */
>
> s/segment addr/segment/, plus it's abot E-DCC compliance as I understand
> it,
> not DDC.
>
> > +               if (!segment)
> > +                       ret = i2c_transfer(adapter, &msgs[1], xfers);
> > +               else
> > +                       ret = i2c_transfer(adapter, msgs, xfers);
> > +
>
> This can be written:
>
>                 ret = i2c_transfer(adapter, &msgs[3 - xfers], xfers);
>
> Which is more compact and, I suspect, faster.
>
> Agreed.

> >                 if (ret == -ENXIO) {
> >                         DRM_DEBUG_KMS("drm: skipping non-existent
> adapter %s\n",
> >                                         adapter->name);
> >                         break;
> >                 }
> > -       } while (ret != 2 && --retries);
> > +       } while (ret != xfers && --retries);
> >
> > -       return ret == 2 ? 0 : -1;
> > +       return ret == xfers ? 0 : -1;
> >  }
> >
> >  static bool drm_edid_is_zero(u8 *in_edid, int length)
>
> Other than this, your code looks reasonable, not so different from what
> I submitted 8 months ago actually. But ISTU you can test the code with
> real hardware while I couldn't.
>
> Your patch never checked for the 3 message transfer complete, it checked
only 2.

With the changes above applied, you can add:
>
> Reviewed-by: Jean Delvare <jdelvare at suse.de>
>
> Will add your review comments in patch set 5 and your reviewed tag.

Thanks & Regards,
Shirish S

> --
> Jean Delvare
> Suse L3
>
> _______________________________________________
> dri-devel mailing list
> dri-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/dri-devel/attachments/20120829/5b818ed7/attachment.html>