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

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Message-ID: <f6e5931a-22ab-4291-b1c5-9885be0b1b22@linux.dev>
Date: Thu, 21 Mar 2024 11:35:14 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Michal Simek <michal.simek@....com>, David Airlie <airlied@...il.com>,
 linux-kernel@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
 linux-arm-kernel@...ts.infradead.org,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 3/8] drm: zynqmp_dp: Adjust training values per-lane

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@...ux.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@...asonboard.com>
> 
>  Tomi
>