[Intel-gfx] [PATCH] drm/i915/bios: Clamp VBT HDMI level shift on BDW

[Nautiyal, Ankit K]

On 10/13/2023 7:32 PM, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> Apparently some BDW machines (eg. HP Pavilion 15-ab) shipped with
> a VBT inherited from some earlier HSW model. On HSW the HDMI level
> shift value could go up to 11, whereas on BDW the maximum value is
> 9.
>
> The DDI code does clamp the bogus value, but it does so with
> a WARN which we don't really want. To avoid that let's just sanitize
> the bogus VBT HDMI level shift value ahead of time for all BDW machines.
>
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/9461
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>   drivers/gpu/drm/i915/display/intel_bios.c | 22 ++++++++++++++++++++++
>   1 file changed, 22 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index 4e8f1e91bb08..8f83f0ead27f 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -2473,6 +2473,27 @@ static void sanitize_device_type(struct intel_bios_encoder_data *devdata,
>   	devdata->child.device_type |= DEVICE_TYPE_NOT_HDMI_OUTPUT;
>   }
>   
> +static void sanitize_hdmi_level_shift(struct intel_bios_encoder_data *devdata,
> +				      enum port port)
> +{
> +	struct drm_i915_private *i915 = devdata->i915;
> +
> +	if (!intel_bios_encoder_supports_dvi(devdata))
> +		return;
> +
> +	/*
> +	 * Some BDW machines (eg. HP Pavilion 15-ab) shipped
> +	 * with a HSW VBT where the level shifter value goes
> +	 * up to 11, whereas the BDW max is 9.

I hope this is just one off case, where incorrect VBT is used.

Verified from Bspec:4299 and _bdw_trans_hdmi entries.

Change looks good to me.

Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>


> +	 */
> +	if (IS_BROADWELL(i915) && devdata->child.hdmi_level_shifter_value > 9) {
> +		drm_dbg_kms(&i915->drm, "Bogus port %c VBT HDMI level shift %d, adjusting to %d\n",
> +			    port_name(port), devdata->child.hdmi_level_shifter_value, 9);
> +
> +		devdata->child.hdmi_level_shifter_value = 9;
> +	}
> +}
> +
>   static bool
>   intel_bios_encoder_supports_crt(const struct intel_bios_encoder_data *devdata)
>   {
> @@ -2652,6 +2673,7 @@ static void parse_ddi_port(struct intel_bios_encoder_data *devdata)
>   	}
>   
>   	sanitize_device_type(devdata, port);
> +	sanitize_hdmi_level_shift(devdata, port);
>   }
>   
>   static bool has_ddi_port_info(struct drm_i915_private *i915)