linux-kernel - Re: [PATCH v3 4/9] drm/bridge: ti-sn65dsi86: Config number of DP lanes Mo' Betta

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Date:   Mon, 3 Feb 2020 15:34:21 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        robdclark@...omium.org, linux-arm-msm@...r.kernel.org,
        seanpaul@...omium.org, Jeffrey Hugo <jeffrey.l.hugo@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Clark <robdclark@...il.com>,
        Jonas Karlman <jonas@...boo.se>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH v3 4/9] drm/bridge: ti-sn65dsi86: Config number of DP
 lanes Mo' Betta

On Wed 18 Dec 14:35 PST 2019, Douglas Anderson wrote:

> The driver used to say that the value to program into bridge register
> 0x93 was dp_lanes - 1.  Looking at the datasheet for the bridge, this
> is wrong.  The data sheet says:
> * 1 = 1 lane
> * 2 = 2 lanes
> * 3 = 4 lanes
> 
> A more proper way to express this encoding is min(dp_lanes, 3).
> 
> At the moment this change has zero effect because we've hardcoded the
> number of DP lanes to 4.  ...and (4 - 1) == min(4, 3).  How fortunate!
> ...but soon we'll stop hardcoding the number of lanes.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> Tested-by: Rob Clark <robdclark@...il.com>
> Reviewed-by: Rob Clark <robdclark@...il.com>

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

> ---
> 
> Changes in v3: None
> Changes in v2: None
> 
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index ab644baaf90c..d55d19759796 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -523,7 +523,7 @@ static void ti_sn_bridge_enable(struct drm_bridge *bridge)
>  			   CHA_DSI_LANES_MASK, val);
>  
>  	/* DP lane config */
> -	val = DP_NUM_LANES(pdata->dp_lanes - 1);
> +	val = DP_NUM_LANES(min(pdata->dp_lanes, 3));
>  	regmap_update_bits(pdata->regmap, SN_SSC_CONFIG_REG, DP_NUM_LANES_MASK,
>  			   val);
>  
> -- 
> 2.24.1.735.g03f4e72817-goog
>