Hi Bjorn,
On Wed 20 Apr 22, 16:12, Bjorn Andersson wrote:
> Commit '80253168dbfd ("drm: of: Lookup if child node has panel or
> bridge")' introduced the ability to describe a panel under a display
> controller without having to use a graph to connect the controller to
> its single child panel (or bridge).
>
> The implementation of this would find the first non-graph node and
> attempt to acquire the related panel or bridge. This prevents cases
> where any other child node, such as a aux bus for a DisplayPort
> controller, or an opp-table to find the referenced panel.
>
> Commit '67bae5f28c89 ("drm: of: Properly try all possible cases for
> bridge/panel detection")' attempted to solve this problem by not
> bypassing the graph reference lookup before attempting to find the panel
> or bridge.
>
> While this does solve the case where a proper graph reference is
> present, it does not allow the caller to distinguish between a
> yet-to-be-probed panel or bridge and the absence of a reference to a
> panel.
>
> One such case is a DisplayPort controller that on some boards have an
> explicitly described reference to a panel, but on others have a
> discoverable DisplayPort display attached (which doesn't need to be
> expressed in DeviceTree).
>
> This reverts commit '67bae5f28c89 ("drm: of: Properly try all possible
> cases for bridge/panel detection")', as a step towards reverting commit
> '80253168dbfd ("drm: of: Lookup if child node has panel or bridge")'.
>
> Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
Acked-by: Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx>
Cheers,
Paul
> ---
> drivers/gpu/drm/drm_of.c | 99 ++++++++++++++++++++--------------------
> 1 file changed, 49 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
> index f4df344509a8..026e4e29a0f3 100644
> --- a/drivers/gpu/drm/drm_of.c
> +++ b/drivers/gpu/drm/drm_of.c
> @@ -214,29 +214,6 @@ int drm_of_encoder_active_endpoint(struct device_node *node,
> }
> EXPORT_SYMBOL_GPL(drm_of_encoder_active_endpoint);
>
> -static int find_panel_or_bridge(struct device_node *node,
> - struct drm_panel **panel,
> - struct drm_bridge **bridge)
> -{
> - if (panel) {
> - *panel = of_drm_find_panel(node);
> - if (!IS_ERR(*panel))
> - return 0;
> -
> - /* Clear the panel pointer in case of error. */
> - *panel = NULL;
> - }
> -
> - /* No panel found yet, check for a bridge next. */
> - if (bridge) {
> - *bridge = of_drm_find_bridge(node);
> - if (*bridge)
> - return 0;
> - }
> -
> - return -EPROBE_DEFER;
> -}
> -
> /**
> * drm_of_find_panel_or_bridge - return connected panel or bridge device
> * @np: device tree node containing encoder output ports
> @@ -259,44 +236,66 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
> struct drm_panel **panel,
> struct drm_bridge **bridge)
> {
> - struct device_node *node;
> - int ret;
> + int ret = -EPROBE_DEFER;
> + struct device_node *remote;
>
> if (!panel && !bridge)
> return -EINVAL;
> -
> if (panel)
> *panel = NULL;
> - if (bridge)
> - *bridge = NULL;
> -
> - /* Check for a graph on the device node first. */
> - if (of_graph_is_present(np)) {
> - node = of_graph_get_remote_node(np, port, endpoint);
> - if (node) {
> - ret = find_panel_or_bridge(node, panel, bridge);
> - of_node_put(node);
> -
> - if (!ret)
> - return 0;
> - }
> - }
>
> - /* Otherwise check for any child node other than port/ports. */
> - for_each_available_child_of_node(np, node) {
> - if (of_node_name_eq(node, "port") ||
> - of_node_name_eq(node, "ports"))
> + /**
> + * 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;
>
> - ret = find_panel_or_bridge(node, panel, bridge);
> - of_node_put(node);
> + goto of_find_panel_or_bridge;
> + }
> +
> + /*
> + * 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;
> +
> + if (panel) {
> + *panel = of_drm_find_panel(remote);
> + if (!IS_ERR(*panel))
> + ret = 0;
> + else
> + *panel = NULL;
> + }
> +
> + /* 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)
> - return 0;
> }
>
> - return -EPROBE_DEFER;
> + of_node_put(remote);
> + return ret;
> }
> EXPORT_SYMBOL_GPL(drm_of_find_panel_or_bridge);
>
> --
> 2.35.1
>
--
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com
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