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Date: Thu, 10 Mar 2022 15:54:23 +0100
From: Maxime Ripard <maxime@...no.tech>
To: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
Linus Walleij <linus.walleij@...aro.org>,
Jagan Teki <jagan@...rulasolutions.com>
Subject: Re: [PATCH] drm: of: Properly try all possible cases for
bridge/panel detection
Hi Paul,
On Wed, Mar 09, 2022 at 03:32:00PM +0100, Paul Kocialkowski wrote:
> While bridge/panel detection was initially relying on the usual
> port/ports-based of graph detection, it was recently changed to
> perform the lookup on any child node that is not port/ports
> instead when such a node is available, with no fallback on the
> usual way.
>
> This results in breaking detection when a child node is present
> but does not contain any panel or bridge node, even when the
> usual port/ports-based of graph is there.
>
> In order to support both situations properly, this commit reworks
> the logic to try both options and not just one of the two: it will
> only return -EPROBE_DEFER when both have failed.
>
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> Fixes: 80253168dbfd ("drm: of: Lookup if child node has panel or bridge")
Thanks, it's in pretty good shape now, but I have a few bike sheds to paint :)
> ---
> drivers/gpu/drm/drm_of.c | 93 +++++++++++++++++++++-------------------
> 1 file changed, 49 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
> index 9d90cd75c457..67f1b7dfc892 100644
> --- a/drivers/gpu/drm/drm_of.c
> +++ b/drivers/gpu/drm/drm_of.c
> @@ -219,6 +219,35 @@ int drm_of_encoder_active_endpoint(struct device_node *node,
> }
> EXPORT_SYMBOL_GPL(drm_of_encoder_active_endpoint);
>
> +static int drm_of_find_remote_panel_or_bridge(struct device_node *remote,
> + struct drm_panel **panel,
> + struct drm_bridge **bridge)
This function performs its look up directly on the struct device_node
passed as argument, so I don't think the "remote" in the name is great.
Since it's static, we can just call it find_panel_or_bridge, what do you
think?
> +{
> + int ret = -EPROBE_DEFER;
> +
> + if (panel) {
> + *panel = of_drm_find_panel(remote);
> + if (!IS_ERR(*panel))
> + ret = 0;
return 0?
> + else
> + *panel = NULL;
> +
> + }
> +
> + /* No panel found yet, check for a bridge next. */
> + if (bridge) {
> + if (ret) {
And the return above allows to remove that test
> + *bridge = of_drm_find_bridge(remote);
> + if (*bridge)
> + ret = 0;
return 0?
> + } else {
> + *bridge = NULL;
> + }
> +
> + }
> +
> + return ret;
And here we can just return -EPROBE_DEFER
> +}
> +
> /**
> * drm_of_find_panel_or_bridge - return connected panel or bridge device
> * @np: device tree node containing encoder output ports
> @@ -249,57 +278,33 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
> if (panel)
> *panel = NULL;
>
> - /**
> - * Devices can also be child nodes when we also control that device
> - * through the upstream device (ie, MIPI-DCS for a MIPI-DSI device).
> - *
> - * Lookup for a child node of the given parent that isn't either port
> - * or ports.
> - */
> - for_each_available_child_of_node(np, remote) {
> - if (of_node_name_eq(remote, "port") ||
> - of_node_name_eq(remote, "ports"))
> - continue;
> -
> - goto of_find_panel_or_bridge;
> + /* Check for a graph on the device node first. */
> + if (of_graph_is_present(np)) {
> + remote = of_graph_get_remote_node(np, port, endpoint);
> + if (remote) {
> + ret = drm_of_find_remote_panel_or_bridge(remote, panel,
> + bridge);
> + of_node_put(remote);
> + }
> }
>
> - /*
> - * of_graph_get_remote_node() produces a noisy error message if port
> - * node isn't found and the absence of the port is a legit case here,
> - * so at first we silently check whether graph presents in the
> - * device-tree node.
> - */
> - if (!of_graph_is_present(np))
> - return -ENODEV;
> -
> - remote = of_graph_get_remote_node(np, port, endpoint);
> -
> -of_find_panel_or_bridge:
> - if (!remote)
> - return -ENODEV;
> + /* Otherwise check for any child node other than port/ports. */
> + if (ret) {
> + for_each_available_child_of_node(np, remote) {
> + if (of_node_name_eq(remote, "port") ||
> + of_node_name_eq(remote, "ports"))
> + continue;
>
> - if (panel) {
> - *panel = of_drm_find_panel(remote);
> - if (!IS_ERR(*panel))
> - ret = 0;
> - else
> - *panel = NULL;
> - }
> + ret = drm_of_find_remote_panel_or_bridge(remote, panel,
> + bridge);
> + of_node_put(remote);
>
> - /* No panel found yet, check for a bridge next. */
> - if (bridge) {
> - if (ret) {
> - *bridge = of_drm_find_bridge(remote);
> - if (*bridge)
> - ret = 0;
> - } else {
> - *bridge = NULL;
> + /* Stop at the first found occurrence. */
> + if (!ret)
> + break;
> }
> -
> }
>
> - of_node_put(remote);
> return ret;
> }
So the diff is fairly hard to read, but it ends up as:
> int ret = -EPROBE_DEFER;
> struct device_node *remote;
>
> if (!panel && !bridge)
> return -EINVAL;
> if (panel)
> *panel = NULL;
>
> /* Check for a graph on the device node first. */
> if (of_graph_is_present(np)) {
> remote = of_graph_get_remote_node(np, port, endpoint);
> if (remote) {
> ret = drm_of_find_remote_panel_or_bridge(remote, panel,
> bridge);
> of_node_put(remote);
I think we can simplify this by doing
if (!ret)
return ret;
> }
> }
>
> /* Otherwise check for any child node other than port/ports. */
> if (ret) {
And thus we won't have to check for ret here
> for_each_available_child_of_node(np, remote) {
I'm a bit reluctant with variables that we reuse from one loop to
another, especially since it's a bit misleading here. What about using a
(loop local) remote variable in the of_graph path, and a loop-local
variable node or child here?
> if (of_node_name_eq(remote, "port") ||
> of_node_name_eq(remote, "ports"))
> continue;
>
> ret = drm_of_find_remote_panel_or_bridge(remote, panel,
> bridge);
> of_node_put(remote);
>
> /* Stop at the first found occurrence. */
> if (!ret)
> break;
Ditto, let's just return here
> }
> }
>
> return ret;
And then we can just return EPROBE_DEFER here (and get rid of ret entirely)
Maxime
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