[PATCH 1/4] drm/panel: use fwnode based lookups for panel followers

[Doug Anderson]

Hi,

On Fri, Jun 6, 2025 at 2:06 AM Jani Nikula <jani.nikula at intel.com> wrote:
>
> Use firmware node based lookups for panel followers, to make the code
> independent of OF and device tree, and make it work also for ACPI with
> an appropriate _DSD.
>
> ASL example:
>
>         Package (0x02)
>         {
>                 "panel", \_SB.PCI0.GFX0.LCD0
>         }
>
> Suggested-by: Heikki Krogerus <heikki.krogerus at linux.intel.com>
> Cc: Neil Armstrong <neil.armstrong at linaro.org>
> Cc: Jessica Zhang <jessica.zhang at oss.qualcomm.com>
> Cc: Maxime Ripard <mripard at kernel.org>
> Cc: Doug Anderson <dianders at chromium.org>
> Cc: Lee Shawn C <shawn.c.lee at intel.com>
> Signed-off-by: Jani Nikula <jani.nikula at intel.com>
> ---
>  drivers/gpu/drm/drm_panel.c | 39 +++++++++++++++++++++++++++++--------
>  1 file changed, 31 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index fee65dc65979..3eb0a615f7a9 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -473,17 +473,40 @@ int of_drm_get_panel_orientation(const struct device_node *np,
>  EXPORT_SYMBOL(of_drm_get_panel_orientation);
>  #endif
>
> -static struct drm_panel *of_find_panel(struct device *follower_dev)
> +/* Find panel by fwnode */
> +static struct drm_panel *find_panel_by_fwnode(const struct fwnode_handle *fwnode)

nit: It might be worth adding a comment that says it should be
identical to of_drm_find_panel() since that has a much richer
kerneldoc that talks about the corner cases.

>  {
> -       struct device_node *panel_np;
>         struct drm_panel *panel;
>
> -       panel_np = of_parse_phandle(follower_dev->of_node, "panel", 0);
> -       if (!panel_np)
> +       if (!fwnode_device_is_available(fwnode))
>                 return ERR_PTR(-ENODEV);
>
> -       panel = of_drm_find_panel(panel_np);
> -       of_node_put(panel_np);
> +       mutex_lock(&panel_lock);
> +
> +       list_for_each_entry(panel, &panel_list, list) {
> +               if (dev_fwnode(panel->dev) == fwnode) {
> +                       mutex_unlock(&panel_lock);
> +                       return panel;
> +               }
> +       }
> +
> +       mutex_unlock(&panel_lock);
> +
> +       return ERR_PTR(-EPROBE_DEFER);
> +}
> +
> +/* Find panel by follower device */
> +static struct drm_panel *find_panel_by_dev(struct device *follower_dev)
> +{
> +       struct fwnode_handle *fwnode;
> +       struct drm_panel *panel;
> +
> +       fwnode = fwnode_find_reference(dev_fwnode(follower_dev), "panel", 0);
> +       if (IS_ERR_OR_NULL(fwnode))

nit: why IS_ERR_OR_NULL() instead of IS_ERR()? The kerneldoc for
fwnode_find_reference() doesn't mention anything about it returning a
NULL value in any cases...

Other than the nits, this looks reasonable to me.

Reviewed-by: Douglas Anderson <dianders at chromium.org>

I no longer have any easy access to hardware where panel-follower is
truly necessary, but I can at least see the panel-follower calls
getting made on sc7180-trogdor-lazor, so the of->fwnode conversion
stuff must be working.

Tested-by: Douglas Anderson <dianders at chromium.org>