RE: [PATCH v3 1/8] drm/i915/backlight: Use default/max brightness for VESA AUX backlight init

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 04 Mar 2026, "Kandpal, Suraj" <suraj.kandpal@intel.com> wrote:
> I did some more digging and for aux_set enabled we really do not need to do get_backlight 
> And read register again that is filled in probe state and fills up the current_level variable that can be use.
> Check drm_edp_backlight_probe_state.
> I also found this little comment there
>
>         /*
>          * If we're not in DPCD control mode yet, the programmed brightness value is meaningless and
>          * the driver should assume max brightness
>          */
>         return bl->max;
>
> So this was a policy that was decided during VESA AUX Backlight implementation time. Also that Mode will not be DPCD
> Initially and will change later during backlight enable so we get to assume max brightness . That should be okay to do with
> Luminance_set case too then.

The comment says, if the panel is not in DPCD control mode, the value in
DPCD is meaningless.

Ditto, if the panel is not in luminance control mode (or whatever the
specific name for it is), the luminance value in DPCD is meaningless.

However, if the panel is in DPCD control mode but not in luminance
control mode, we should be able to read the non-luminance DPCD
brightness value and use that.

BR,
Jani.


-- 
Jani Nikula, Intel