Re: [PATCH] drm: Add DPCD definitions for DP 1.4 FEC feature

[Manasi Navare <manasi.d.navare@intel.com>]

On Mon, Nov 27, 2017 at 04:55:44PM -0800, Anusha Srivatsa wrote:
> Forward Error Correction is supported on DP 1.4.
> This patch adds corresponding DPCD register definitions.
> 
> v2: Add dri-devel to the CC list
> 
> Cc: dri-devel@lists.freedesktop.org
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
> ---
>  include/drm/drm_dp_helper.h | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index da58a42..bc816ea 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -284,6 +284,35 @@
>  # define DP_DSC_BITS_PER_PIXEL_1_2          0x3
>  # define DP_DSC_BITS_PER_PIXEL_1            0x4
>  
> +/* DP Forward error Correction Registers */
> +#define DP_FEC_CAPABILITY		    0x090
> +# define DP_FEC_CAPABLE			    (1 << 0)
> +# define DP_FEC_UNCORR_BLK_ERROR_COUNT_CAP  (1 << 1)
> +# define DP_FEC_CORR_BLK_ERROR_COUNT_CAP    (1 << 2)
> +# define DP_FEC_BIT_ERROR_COUNT_CAP	    (1 << 3)
> +
> +#define DP_FEC_CONFIGURATION		    0x120
> +# define DP_FEC_READY			    (1 << 0)
> +# define DP_FEC_ERR_COUNT_DIS		    (0 << 1)
> +# define DP_FEC_UNCORR_BLK_ERROR_COUNT	    (1 << 1)
> +# define DP_FEC_CORR_BLK_ERROR_COUNT	    (2 << 1)
> +# define DP_FEC_BIT_ERROR_COUNT		    (3 << 1)

These above values indicate the value of FEC_ERROR_COUNT_SEL.
I think we would need a mask for FEC_ERROR_COUNT_SEL field so that
we can read this field as drm_dpcd_read(DP_FEC_CONFIGURATION) & FEC_ERROR_COUNT_SEL_MASK
and then compare this to each of the values for that field.
So we would need an extra #define for the MASK

> +# define DP_FEC_LANE_0_SELECT		    (0 << 4)
> +# define DP_FEC_LANE_1_SELECT		    (1 << 4)
> +# define DP_FEC_LANE_2_SELECT		    (2 << 4)
> +# define DP_FEC_LANE_3_SELECT		    (3 << 4)
> +
> +#define DP_FEC_STATUS			    0x280
> +# define DP_FEC_EN_DETECTED		    (1 << 0)

I think better name would be DP_FEC_DECODE_EN_DETECTED since this refers
to FEC_DECODE_EN link symbol sequence

> +# define DP_FEC_DEC_DETECTED		    (1 << 1)

And this should be DP_FEC_DECODE_DIS_DETECTED since this refers to
FEC_DECODE_DIS link symbol sequence

> +
> +#define DP_FEC_ERROR_COUNT_1		    0x0281
> +# define DP_FEC_ERR_COUNT_7_0(err_count)    (err_count << 0)

So this is a RO register and so we wont be writing the err_count by passing it as
an argument as above.
And this is the entire reister that indicates the LSB of ERR_COUNT you can just rename the
register as DP_FEC_ERR_COUNT_LSB
So while reading you just pass this register address and get LSB into a variable.

> +
> +#define DP_FEC_ERROR_COUNT_2		    0x0282
> +# define DP_FEC_ERR_COUNT_14_8(err_count)   (err_count << 0)

This could be DP_FEC_ERR_COUNT_MSB_MASK and SHIFT should be 8 since
you want to put this value at the 8th bit of a 16 bit value.

> +# define DP_FEC_ERR_COUNT_VALID		    (1 << 7)

Everything else looks good.

Manasi

> +
>  #define DP_PSR_SUPPORT                      0x070   /* XXX 1.2? */
>  # define DP_PSR_IS_SUPPORTED                1
>  # define DP_PSR2_IS_SUPPORTED		    2	    /* eDP 1.4 */
> -- 
> 2.7.4
> 
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