linux-kernel - Re: [PATCH 2/6] drm: zynqmp_dp: Adjust training values per-lane

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Date: Mon, 18 Mar 2024 19:06:09 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	dri-devel@...ts.freedesktop.org, David Airlie <airlied@...il.com>,
	linux-kernel@...r.kernel.org, Michal Simek <michal.simek@....com>,
	linux-arm-kernel@...ts.infradead.org,
	Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 2/6] drm: zynqmp_dp: Adjust training values per-lane

Hi Sean,

Thank you for the patch.

On Fri, Mar 15, 2024 at 07:09:12PM -0400, 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>
> ---
> 
>  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;
> +	}

I don't have enough DP knowledge to review this :-(

>  }
>  
>  /**

-- 
Regards,

Laurent Pinchart