linux-kernel - Re: [PATCH v2 2/2] drm/bridge: parade-ps8640: Populate devices on aux-bus

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Date:   Mon, 25 Oct 2021 13:10:01 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Philip Chen <philipchen@...omium.org>
Cc:     dianders@...omium.org, Andrzej Hajda <a.hajda@...sung.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 2/2] drm/bridge: parade-ps8640: Populate devices on aux-bus

Quoting Philip Chen (2021-10-21 14:06:00)
> diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
> index 220ca3b03d24..f99a2e0808b7 100644
> --- a/drivers/gpu/drm/bridge/parade-ps8640.c
> +++ b/drivers/gpu/drm/bridge/parade-ps8640.c
> @@ -149,6 +150,23 @@ static inline struct ps8640 *aux_to_ps8640(struct drm_dp_aux *aux)
>         return container_of(aux, struct ps8640, aux);
>  }
>
> +static bool ps8640_of_panel_on_aux_bus(struct device *dev)
> +{
> +       struct device_node *bus, *panel;
> +
> +       bus = of_get_child_by_name(dev->of_node, "aux-bus");
> +       if (!bus)
> +               return false;
> +       of_node_put(bus);

This should come after the next line...

> +
> +       panel = of_get_child_by_name(bus, "panel");

here, so that 'bus' can't go away before getting children nodes. It
doesn't actually matter in this case because 'device' holds the aux-bus,
but we shouldn't add anti-patterns to the code lest someone copies it
where it actually matters.

> +       if (!panel)
> +               return false;
> +       of_node_put(panel);
> +
> +       return true;
> +}
> +
>  static void ps8640_ensure_hpd(struct ps8640 *ps_bridge)
>  {
>         struct regmap *map = ps_bridge->regmap[PAGE2_TOP_CNTL];

Otherwise

Reviewed-by: Stephen Boyd <swboyd@...omium.org>