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

[Daniel Vetter]

On Sat, Aug 25, 2012 at 03:13:56PM +0530, Shirish S 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>

Looks good.

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

> ---
>  drivers/gpu/drm/drm_edid.c |   22 ++++++++++++++++++----
>  1 files changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index a8743c3..cde7af0 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 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,
> +				.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.
> +	 */
> +		if (!segment)
> +			ret = i2c_transfer(adapter, &msgs[1], xfers);
> +		else
> +			ret = i2c_transfer(adapter, msgs, xfers);
> +
>  		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)
> -- 
> 1.7.0.4
> 
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-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48