Re: [PATCH v2 3/8] drm: zynqmp_dp: Adjust training values per-lane

Sean Anderson
2024-03-21T15:35:23Z

On 3/20/24 01:57, Tomi Valkeinen wrote:
> On 20/03/2024 00:51, Sean Anderson wrote:
>> The feedback we get from the DPRX is per-lane. Make changes using this
>> information, instead of picking the maximum values from all lanes. This
>> results in more-consistent training on marginal links.
>>
>> Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
>> ---
>>
>> (no changes since v1)
>>
>> drivers/gpu/drm/xlnx/zynqmp_dp.c | 23 ++++++++---------------
>> 1 file changed, 8 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
>> index 98a32e6a0459..8635b5673386 100644
>> --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
>> +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
>> @@ -605,28 +605,21 @@ static void zynqmp_dp_adjust_train(struct zynqmp_dp *dp,
>> u8 link_status[DP_LINK_STATUS_SIZE])
>> {
>> u8 *train_set = dp->train_set;
>> - u8 voltage = 0, preemphasis = 0;
>> u8 i;
>> for (i = 0; i < dp->mode.lane_cnt; i++) {
>> - u8 v = drm_dp_get_adjust_request_voltage(link_status, i);
>> - u8 p = drm_dp_get_adjust_request_pre_emphasis(link_status, i);
>> + u8 voltage = drm_dp_get_adjust_request_voltage(link_status, i);
>> + u8 preemphasis =
>> + drm_dp_get_adjust_request_pre_emphasis(link_status, i);
>> - if (v > voltage)
>> - voltage = v;
>> + if (voltage >= DP_TRAIN_VOLTAGE_SWING_LEVEL_3)
>> + voltage |= DP_TRAIN_MAX_SWING_REACHED;
>> - if (p > preemphasis)
>> - preemphasis = p;
>> - }
>> + if (preemphasis >= DP_TRAIN_PRE_EMPH_LEVEL_2)
>> + preemphasis |= DP_TRAIN_MAX_PRE_EMPHASIS_REACHED;
>> - if (voltage >= DP_TRAIN_VOLTAGE_SWING_LEVEL_3)
>> - voltage |= DP_TRAIN_MAX_SWING_REACHED;
>> -
>> - if (preemphasis >= DP_TRAIN_PRE_EMPH_LEVEL_2)
>> - preemphasis |= DP_TRAIN_MAX_PRE_EMPHASIS_REACHED;
>> -
>> - for (i = 0; i < dp->mode.lane_cnt; i++)
>> train_set[i] = voltage | preemphasis;
>> + }
>> }
>> /**
>
> Looks fine to me, but a few cosmetic suggestions, feel free to ignore if not to your liking:
>
> 1)
>
> u8 voltage, preemphasis;
>
> voltage = drm_dp_get_adjust_request_voltage(link_status, i);
> preemphasis = drm_dp_get_adjust_request_pre_emphasis(link_status, i);

If the comment here is about the line break, I agree that this looks
better but the second line is over 80 characters.

> 2)
>
> for (unsigned int i = 0; i < dp->mode.lane_cnt; i++)

Is this allowed now?

> 3)
>
> dp->train_set[i] = voltage | preemphasis;

This would be undone in patch 7/8.

--Sean

> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
>
> Tomi
>