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

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Message-ID: <c16665d3-ff3a-48d7-9f4e-076473a3b45d@ideasonboard.com>
Date: Wed, 20 Mar 2024 07:57:48 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Sean Anderson <sean.anderson@...ux.dev>
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 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);

2)

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

3)

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


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

  Tomi