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

[Srivatsa, Anusha]

>-----Original Message-----
>From: Navare, Manasi D
>Sent: Thursday, December 21, 2017 12:36 PM
>To: Srivatsa, Anusha <anusha.srivatsa at intel.com>
>Cc: intel-gfx at lists.freedesktop.org; dri-devel at lists.freedesktop.org; Ville Syrjala
><ville.syrjala at linux.intel.com>; Jani Nikula <jani.nikula at linux.intel.com>
>Subject: Re: [PATCH] drm: Add DPCD definitions for DP 1.4 FEC feature
>
>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 at lists.freedesktop.org
>> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
>> Cc: Jani Nikula <jani.nikula at linux.intel.com>
>> Cc: Manasi Navare <manasi.d.navare at intel.com>
>> Signed-off-by: Anusha Srivatsa <anusha.srivatsa at 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

Sounds good.... 

>> +# 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

Now that you mentioned, I noticed that's the name used in spec too. I wonder why I went ahead with the above name. Shall change it. Thanks.

>> +# 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.

Yes, good point.

>
>> +
>> +#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.

This helps.... thanks!

>> +# define DP_FEC_ERR_COUNT_VALID		    (1 << 7)
>
>Everything else looks good.

Thanks Manasi. I will incorporate these changes in the next revision.

Anusha 
>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
>>