Re: [PATCH v5 3/4] drm/i915/dp: Allow forcing specific interfaces through enable_dpcd_backlight

Jani Nikula
2021-01-11T19:08:19Z

On Thu, 07 Jan 2021, Lyude Paul <lyude@redhat.com> wrote:
> Since we now support controlling panel backlights through DPCD using
> both the standard VESA interface, and Intel's proprietary HDR backlight
> interface, we should allow the user to be able to explicitly choose
> between one or the other in the event that we're wrong about panels
> reliably reporting support for the Intel HDR interface.
>
> So, this commit adds support for this by introducing two new
> enable_dpcd_backlight options: 2 which forces i915 to only probe for the
> VESA interface, and 3 which forces i915 to only probe for the Intel
> backlight interface (might be useful if we find panels in the wild that
> report the VESA interface in their VBT, but actually only support the
> Intel backlight interface).
>
> v3:
> * Rebase
>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>

Yup. Feels maybe a bit convoluted, but I'll trust your judgement as
you've been playing with these.

BR,
Jani.

> Cc: thaytan@noraisin.net
> Cc: Vasily Khoruzhick <anarsoul@gmail.com>
> ---
> .../drm/i915/display/intel_dp_aux_backlight.c | 45 +++++++++++++++++--
> drivers/gpu/drm/i915/i915_params.c | 2 +-
> 2 files changed, 43 insertions(+), 4 deletions(-)
>
> 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 5e761fb49a14..4b2cb20b1f94 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -613,15 +613,54 @@ static const struct intel_panel_bl_funcs intel_dp_vesa_bl_funcs = {
> .get = intel_dp_aux_vesa_get_backlight,
> };
>
> +enum intel_dp_aux_backlight_modparam {
> + INTEL_DP_AUX_BACKLIGHT_AUTO = -1,
> + INTEL_DP_AUX_BACKLIGHT_OFF = 0,
> + INTEL_DP_AUX_BACKLIGHT_ON = 1,
> + INTEL_DP_AUX_BACKLIGHT_FORCE_VESA = 2,
> + INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL = 3,
> +};
> +
> int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
> {
> struct drm_device *dev = connector->base.dev;
> struct intel_panel *panel = &connector->panel;
> struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> + bool try_intel_interface = false, try_vesa_interface = false;
>
> - if (i915->params.enable_dpcd_backlight == 0)
> + /* Check the VBT and user's module parameters to figure out which
> + * interfaces to probe
> + */
> + switch (i915->params.enable_dpcd_backlight) {
> + case INTEL_DP_AUX_BACKLIGHT_OFF:
> return -ENODEV;
> + case INTEL_DP_AUX_BACKLIGHT_AUTO:
> + switch (i915->vbt.backlight.type) {
> + case INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE:
> + try_vesa_interface = true;
> + break;
> + case INTEL_BACKLIGHT_DISPLAY_DDI:
> + try_intel_interface = true;
> + try_vesa_interface = true;
> + break;
> + default:
> + return -ENODEV;
> + }
> + break;
> + case INTEL_DP_AUX_BACKLIGHT_ON:
> + if (i915->vbt.backlight.type != INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE)
> + try_intel_interface = true;
> +
> + try_vesa_interface = true;
> + break;
> + case INTEL_DP_AUX_BACKLIGHT_FORCE_VESA:
> + try_vesa_interface = true;
> + break;
> + case INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL:
> + try_intel_interface = true;
> + break;
> + }
>
> /*
> * A lot of eDP panels in the wild will report supporting both the
> @@ -630,13 +669,13 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
> * and will only work with the Intel interface. So, always probe for
> * that first.
> */
> - if (intel_dp_aux_supports_hdr_backlight(connector)) {
> + if (try_intel_interface && intel_dp_aux_supports_hdr_backlight(connector)) {
> drm_dbg_kms(dev, "Using Intel proprietary eDP backlight controls\n");
> panel->backlight.funcs = &intel_dp_hdr_bl_funcs;
> return 0;
> }
>
> - if (intel_dp_aux_supports_vesa_backlight(connector)) {
> + if (try_vesa_interface && intel_dp_aux_supports_vesa_backlight(connector)) {
> drm_dbg_kms(dev, "Using VESA eDP backlight controls\n");
> panel->backlight.funcs = &intel_dp_vesa_bl_funcs;
> return 0;
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index 7f139ea4a90b..6939634e56ed 100644
> --- a/drivers/gpu/drm/i915/i915_params.c
> +++ b/drivers/gpu/drm/i915/i915_params.c
> @@ -185,7 +185,7 @@ i915_param_named_unsafe(inject_probe_failure, uint, 0400,
>
> i915_param_named(enable_dpcd_backlight, int, 0400,
> "Enable support for DPCD backlight control"
> - "(-1=use per-VBT LFP backlight type setting [default], 0=disabled, 1=enabled)");
> + "(-1=use per-VBT LFP backlight type setting [default], 0=disabled, 1=enable, 2=force VESA interface, 3=force Intel interface)");
>
> #if IS_ENABLED(CONFIG_DRM_I915_GVT)
> i915_param_named(enable_gvt, bool, 0400,