Hi Jagan,
Thank you for the patch.
On Mon, Dec 13, 2021 at 05:46:13PM +0530, Jagan Teki wrote:
> Some OF graphs don't require 'ports' to represent the
> downstream panel or bridge; instead it simply adds a child
> node on a given parent node.
>
> drm_of_find_panel_or_bridge can lookup panel or bridge for
> a given node based on the OF graph port and endpoint and it
> fails to use if the given node has a child panel or bridge.
>
> This patch add support to lookup that given node has child
> panel or bridge however that child node cannot be a 'port'
> alone or it cannot be a 'port' node too.
>
> Example OF graph representation of DSI host, which doesn't
> have 'ports' and has child panel.
>
> dsi {
> compatible = "allwinner,sun6i-a31-mipi-dsi";
> #address-cells = <1>;
> #size-cells = <0>;
>
> port {
> dsi_in_tcon0: endpoint {
> remote-endpoint = <tcon0_out_dsi>;
> };
>
> panel@0 {
> reg = <0>;
> };
> };
>
> Example OF graph representation of DSI host, which doesn't
> have 'ports' and has child bridge.
>
> dsi {
> compatible = "allwinner,sun6i-a31-mipi-dsi";
> #address-cells = <1>;
> #size-cells = <0>;
>
> port {
> dsi_in_tcon0: endpoint {
> remote-endpoint = <tcon0_out_dsi>;
> };
>
> bridge@0 {
> reg = <0>;
>
> ports {
> #address-cells = <1>;
> #size-cells = <0>;
>
> bridge_out: port@1 {
> reg = <1>;
>
> bridge_out_panel: endpoint {
> remote-endpoint = <&panel_out_bridge>;
> };
> };
> };
> };
> };
>
> Example OF graph representation of DSI host, which doesn't
> have 'ports' or 'port' and has child panel.
>
> dsi0 {
> compatible = "ste,mcde-dsi";
> #address-cells = <1>;
> #size-cells = <0>;
>
> panel@0 {
> reg = <0>;
> };
> };
>
> Example OF graph representation of LTDC host, which doesn't
> have 'ports' or child panel/bridge and has 'port'.
>
> ltdc {
> compatible = "st,stm32-ltdc";
> #address-cells = <1>;
> #size-cells = <0>;
>
> port {
> };
> };
>
> Signed-off-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>
> ---
> Changes for v2:
> - drop of helper
> https://patchwork.kernel.org/project/dri-devel/cover/20211207054747.461029-1-jagan@xxxxxxxxxxxxxxxxxxxx/
> - support 'port' alone OF graph
> - updated comments
> - added simple code
>
> drivers/gpu/drm/drm_of.c | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
> index 59d368ea006b..7d018ff8bc83 100644
> --- a/drivers/gpu/drm/drm_of.c
> +++ b/drivers/gpu/drm/drm_of.c
> @@ -249,6 +249,27 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
> if (panel)
> *panel = NULL;
>
> + /**
> + * Some OF graphs don't require 'ports' to represent the downstream
> + * panel or bridge; instead it simply adds a child node on a given
> + * parent node.
> + *
> + * Lookup that child node for a given parent however that child
> + * cannot be a 'port' alone or it cannot be a 'port' node too.
> + */
> + if (!of_get_child_by_name(np, "ports")) {
> + if (of_get_child_by_name(np, "port") && (of_get_child_count(np) == 1))
This messes up reference counting of device_node.
> + goto of_graph_get_remote;
> +
> + for_each_available_child_of_node(np, remote) {
> + if (of_node_name_eq(remote, "port"))
> + continue;
> +
> + goto of_find_panel_or_bridge;
> + }
> + }
This really looks like a hack to me, I'm worried it may cause issues. It
would be better, I think, to split the drm_of_find_panel_or_bridge()
function in two, with the of_graph_get_remote_node() call moved to a
wrapper function, calling an inner function that takes the remote
device_node pointer. For the DSI use case, you could either look up the
panel DT node in the display driver and call the inner function
directly, or implement a DSI-specific wrapper.
> +
> +of_graph_get_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,
> @@ -259,6 +280,8 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
> return -ENODEV;
>
> remote = of_graph_get_remote_node(np, port, endpoint);
> +
> +of_find_panel_or_bridge:
> if (!remote)
> return -ENODEV;
>
--
Regards,
Laurent Pinchart
