[PATCH] drm: of: Properly try all possible cases for bridge/panel detection
Paul Kocialkowski
paul.kocialkowski at bootlin.com
Wed Mar 16 15:40:49 UTC 2022
Hi Maxime,
Thanks for the review!
On Thu 10 Mar 22, 15:54, Maxime Ripard wrote:
> 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 at bootlin.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?
From a quick look at other DRM code I got the impression that static functions
also usually carry the drm prefix but I might be wrong.
> > +{
> > + int ret = -EPROBE_DEFER;
> > +
> > + if (panel) {
> > + *panel = of_drm_find_panel(remote);
> > + if (!IS_ERR(*panel))
> > + ret = 0;
>
> return 0?
The idea was to still go through the "*bridge = NULL;" path if a bridge
pointer is provided, to preserve the original behavior of the function.
There may or may not not be any hard expectation on that, in any case
I feel like it would be good to avoid out-of-scope functional changes here.
> > + 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:
Yeah I agree, not sure what I can do about that.
> > 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
Yes I agree this one makes things more readable.
> > 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?
I feel like reusing variables across loops is quite a common thing and
not really an issue on its own, but I agree that calling this one remote
is confusing and "child" would make things clearer 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
Sure, fair enough!
> > }
> > }
> >
> > return ret;
>
> And then we can just return EPROBE_DEFER here (and get rid of ret entirely)
Sounds good to me, thanks!
Paul
--
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com
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