linux-kernel - Re: [PATCH v1] drm/msm: use compatible string to find mdp node

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Date:   Tue, 5 Oct 2021 11:06:33 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Krishna Manikandan <mkrishn@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     kalyan_t@...eaurora.org, robdclark@...il.com,
        bjorn.andersson@...aro.org, freedreno@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v1] drm/msm: use compatible string to find mdp node

Quoting Krishna Manikandan (2021-10-05 02:44:31)
> In the current implementation, substring comparison
> using device node name is used to find mdp node
> during driver probe. Use compatible string instead
> of node name to get mdp node from the parent mdss node.
>
> Signed-off-by: Krishna Manikandan <mkrishn@...eaurora.org>
> ---
>  drivers/gpu/drm/msm/msm_drv.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index 2e6fc18..50a23cf 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -1241,9 +1241,16 @@ static int add_components_mdp(struct device *mdp_dev,
>         return 0;
>  }
>
> -static int compare_name_mdp(struct device *dev, void *data)
> +static int find_mdp_node(struct device *dev, void *data)
>  {
> -       return (strstr(dev_name(dev), "mdp") != NULL);
> +       return of_device_is_compatible(dev->of_node, "qcom,mdp4") ||

Why do we care about mdp4? It looks like this function is only called if
get_mdp_ver() returns 5 or DPU, in which case 4 isn't relevant?

> +               of_device_is_compatible(dev->of_node, "qcom,mdp5") ||
> +               of_device_is_compatible(dev->of_node, "qcom,mdss_mdp") ||
> +               of_device_is_compatible(dev->of_node, "qcom,sdm845-dpu") ||
> +               of_device_is_compatible(dev->of_node, "qcom,sm8150-dpu") ||
> +               of_device_is_compatible(dev->of_node, "qcom,sm8250-dpu") ||
> +               of_device_is_compatible(dev->of_node, "qcom,sc7180-dpu") ||
> +               of_device_is_compatible(dev->of_node, "qcom,sc7280-dpu");

Instead of this duplicate string check why not use canonical compatible
lists?

	return of_match_node(dpu_dt_match, dev->of_node) ||
	       of_match_node(mdp5_dt_match, dev->of_node);


This way we're not constantly updating this list of compatibles in two
places.

>  }
>
>  static int add_display_components(struct platform_device *pdev,
> @@ -1268,7 +1275,7 @@ static int add_display_components(struct platform_device *pdev,
>                         return ret;
>                 }
>
> -               mdp_dev = device_find_child(dev, NULL, compare_name_mdp);
> +               mdp_dev = device_find_child(dev, NULL, find_mdp_node);
>                 if (!mdp_dev) {
>                         DRM_DEV_ERROR(dev, "failed to find MDSS MDP node\n");
>                         of_platform_depopulate(dev);