linux-kernel - Re: [PATCH v5 14/14] drm/msm/dp: Add support for lane mapping configuration

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Message-ID: <j7ooyi5vih6ofnjigdgj6uk3ycutugunpm5pu5zf55pu5ua6r2@agg73zakjicn>
Date: Fri, 19 Sep 2025 21:35:55 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Xiangxu Yin <xiangxu.yin@....qualcomm.com>
Cc: Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        fange.zhang@....qualcomm.com, yongxing.mou@....qualcomm.com,
        li.liu@....qualcomm.com, Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>
Subject: Re: [PATCH v5 14/14] drm/msm/dp: Add support for lane mapping
 configuration

On Fri, Sep 19, 2025 at 10:24:31PM +0800, Xiangxu Yin wrote:
> QCS615 platform requires non-default logical-to-physical lane mapping due
> to its unique hardware routing. Unlike the standard mapping sequence
> <0 1 2 3>, QCS615 uses <3 2 0 1>, which necessitates explicit
> configuration via the data-lanes property in the device tree. This ensures
> correct signal routing between the DP controller and PHY.
> 
> For partial definitions, fill remaining lanes with unused physical lanes
> in ascending order.
> 
> Signed-off-by: Xiangxu Yin <xiangxu.yin@....qualcomm.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 10 +++----
>  drivers/gpu/drm/msm/dp/dp_link.c | 60 ++++++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/msm/dp/dp_link.h |  1 +
>  3 files changed, 66 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_link.c b/drivers/gpu/drm/msm/dp/dp_link.c
> index 2aeb3ecf76fab2ee6a9512b785ca5dceebfc3964..34a91e194a124ef5372f13352f7b3513aa88da2a 100644
> --- a/drivers/gpu/drm/msm/dp/dp_link.c
> +++ b/drivers/gpu/drm/msm/dp/dp_link.c
> @@ -1236,6 +1236,61 @@ static u32 msm_dp_link_link_frequencies(struct device_node *of_node)
>  	return frequency;
>  }
>  
> +/*
> + * Always populate msm_dp_link->lane_map with 4 lanes.
> + * - Use DTS "data-lanes" if present; otherwise fall back to default mapping.
> + * - For partial definitions, fill remaining entries with unused lanes in
> + *   ascending order.
> + */
> +static int msm_dp_link_lane_map(struct device *dev, struct msm_dp_link *msm_dp_link)
> +{
> +	struct device_node *of_node = dev->of_node;
> +	struct device_node *endpoint;
> +	int cnt = msm_dp_link->max_dp_lanes;
> +	u32 tmp[DP_MAX_NUM_DP_LANES];
> +	u32 map[DP_MAX_NUM_DP_LANES] = {0, 1, 2, 3}; /* default 1:1 mapping */
> +	bool used[DP_MAX_NUM_DP_LANES] = {false};
> +	int i, j = 0, ret = -EINVAL;
> +
> +	endpoint = of_graph_get_endpoint_by_regs(of_node, 1, -1);
> +	if (endpoint) {
> +		ret = of_property_read_u32_array(endpoint, "data-lanes", tmp, cnt);
> +		if (ret)
> +			dev_dbg(dev, "endpoint data-lanes read failed (ret=%d)\n", ret);
> +	}
> +
> +	if (ret) {
> +		ret = of_property_read_u32_array(of_node, "data-lanes", tmp, cnt);
> +		if (ret) {
> +			dev_info(dev, "data-lanes not defined, set to default\n");
> +			goto out;
> +		}
> +	}
> +
> +	for (i = 0; i < cnt; i++) {
> +		if (tmp[i] >= DP_MAX_NUM_DP_LANES) {
> +			dev_err(dev, "data-lanes[%d]=%u out of range\n", i, tmp[i]);
> +			return -EINVAL;
> +		}
> +		used[tmp[i]] = true;
> +		map[i] = tmp[i];
> +	}
> +
> +	/* Fill the remaining entries with unused physical lanes (ascending) */
> +	for (i = cnt; i < DP_MAX_NUM_DP_LANES && j < DP_MAX_NUM_DP_LANES; j++) {

Nit: i = cnt, j = 0; Don't init loop variables at the top of the
function.

Other than that:

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>


> +		if (!used[j])
> +			map[i++] = j;
> +	}
> +
> +out:
> +	if (endpoint)
> +		of_node_put(endpoint);
> +
> +	dev_dbg(dev, "data-lanes count %d <%d %d %d %d>\n", cnt, map[0], map[1], map[2], map[3]);
> +	memcpy(msm_dp_link->lane_map, map, sizeof(map));
> +	return 0;
> +}
> +
>  static int msm_dp_link_parse_dt(struct device *dev, struct msm_dp_link *msm_dp_link)
>  {
>  	struct device_node *of_node = dev->of_node;

-- 
With best wishes
Dmitry