[PATCH 4/7] drm/i915/backlight: Modify function to get VESA brightness in Nits

[Murthy, Arun R]

> Modify vesa_get_brightness function to take into account
> luminance_control_support and based on that read the appropriate register
> and return the value.
> 
> --v2
> -Changes since we now use luminance instead of nits
> 
> Signed-off-by: Suraj Kandpal <suraj.kandpal at intel.com>
> Tested-by: Ben Kao <ben.kao at intel.com>
> ---
>  .../drm/i915/display/intel_dp_aux_backlight.c | 20 +++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> index 84126e7d1716..a733b5623563 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -451,6 +451,26 @@ intel_dp_aux_hdr_setup_backlight(struct
> intel_connector *connector, enum pipe pi
>  /* VESA backlight callbacks */
>  static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector *connector,
> enum pipe unused)  {
> +	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> +	struct intel_panel *panel = &connector->panel;
> +	u8 buf[3];
> +	u32 val = 0;
> +	int ret;
> +
> +	if (panel->backlight.edp.vesa.luminance_control_support) {
> +		ret = drm_dp_dpcd_read(&intel_dp->aux,
> DP_EDP_PANEL_TARGET_LUMINANCE_VALUE, buf,
> +				       sizeof(buf));
> +		if (ret < 0) {
> +			drm_err(intel_dp->aux.drm_dev,
> +				"[CONNECTOR:%d:%s] Failed to read
> Luminance from DPCD\n",
> +				connector->base.base.id, connector-
> >base.name);
> +			return 0;
> +		}
> +
> +		val |= buf[0] | buf[1] << 8 | buf[2] << 16;
|= doesn't add any value
Also better to add braces (buf[1] << 8)

> +		return val / 1000;
Fractional value will be lost.
If its expected then with the above said changes
Reviewed-by: Arun R Murthy <arun.r.murthy at intel.com>

Thanks and Regards,
Arun R Murthy
--------------------

> +	}
> +
>  	return connector->panel.backlight.level;  }
> 
> --
> 2.34.1