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

[Daniel Vetter]

On Tue, Aug 21, 2012 at 9:10 AM, Shirish S <s.shirish at samsung.com> wrote:
> The current logic for probing ddc is limited to
> 2 blocks (256 bytes), this patch adds support
> for the 4 block (512) data.
>
> To do this, a single 8-bit segment index is
> passed to the display via the I2C address 30h.
> Data from the selected segment is then immediately
> read via the regular DDC2 address using a repeated
> I2C 'START' signal.
>
> Signed-off-by: Shirish S <s.shirish at samsung.com>
> ---
>  drivers/gpu/drm/drm_edid.c |   17 ++++++++++++-----
>  1 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index a8743c3..2c2996e 100644
> --- 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 short segFlags = segment ? 0 : I2C_M_IGNORE_NAK;

Have you tested this on i915 with gmbus enabled? I'm asking since we
don't implement the IGNORE_NAK flag and hence I'd expect spurious
failures on displays that don't support E-DDC ...

Cheers, Daniel

>         int ret, retries = 5;
>
>         /* The core i2c driver will automatically retry the transfer if the
> @@ -264,27 +266,32 @@ 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  = segFlags,
> +                               .len    = 1,
> +                               .buf    = &start,
> +                       }, { /*set offset */
>                                 .addr   = DDC_ADDR,
>                                 .flags  = 0,
>                                 .len    = 1,
>                                 .buf    = &start,
> -                       }, {
> +                       }, { /*set data */
>                                 .addr   = DDC_ADDR,
>                                 .flags  = I2C_M_RD,
>                                 .len    = len,
>                                 .buf    = buf,
>                         }
>                 };
> -               ret = i2c_transfer(adapter, msgs, 2);
> +               ret = i2c_transfer(adapter, msgs, 3);
>                 if (ret == -ENXIO) {
>                         DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
>                                         adapter->name);
>                         break;
>                 }
> -       } while (ret != 2 && --retries);
> +       } while (ret != 3 && --retries);
>
> -       return ret == 2 ? 0 : -1;
> +       return ret == 3 ? 0 : -1;
>  }
>
>  static bool drm_edid_is_zero(u8 *in_edid, int length)
> --
> 1.7.0.4
>
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-- 
Daniel Vetter
daniel.vetter at ffwll.ch - +41 (0) 79 364 57 48 - http://blog.ffwll.ch