If there is no backlight specified in the device tree and the panel
has access to the DP AUX channel then create a DP AUX backlight if
supported by the panel.

Signed-off-by: Rajeev Nandan <redacted>
---

This patch depends on [1] (drm/panel: panel-simple: Stash DP AUX bus;
allow using it for DDC) and the previous patch (2/5) of this series.

Changes in v4:
- New

Changes in v5:
- Address review comments and move backlight functions to drm_panel.c (Douglas)
- Create and register DP AUX backlight if there is no backlight specified in the
  device tree and panel has the DP AUX channel. (Douglas)
- The new drm_panel_dp_aux_backlight() will do the drm_edp_backlight_supported() check.

[1] https://lore.kernel.org/dri-devel/20210524165920.v8.7.I18e60221f6d048d14d6c50a770b15f356fa75092@changeid/ (local)

 drivers/gpu/drm/panel/panel-simple.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index b09be6e..047fad5 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c

@@ -800,6 +800,12 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc,
        if (err)
                goto disable_pm_runtime;

+       if (!panel->base.backlight && panel->aux) {
+               err = drm_panel_dp_aux_backlight(&panel->base, panel->aux);
+               if (err)
+                       goto disable_pm_runtime;
+       }