Re: [Intel-gfx] [PATCH 2/3] drm/i915/bios: Don't parse the DPS panel type when the VBT does not have it

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

On Wed, 15 Jun 2022, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Older VBTs don't have all the stuff we've defined for the
> LVDS options block (40). In particular we're currently parsing
> the DPS panel type bits even though they may not exist, which
> could mean we end up flagging the machine as supporting static
> DRRS when the VBT declared no such thing.
>
> We don't actually have a clear idea which VBT versions have
> which bits so we rely on the block size instead.
>
> Here's a quick list from my VBT stash:
> mgm version 108 -> 4 bytes
> alv version 120 -> 4 bytes
> cst version 134 -> 14 bytes
> pnv version 144 -> 14 bytes
> cl  version 142 -> 16 bytes
> ctg version 155 -> 24 bytes
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Acked-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_bios.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index df52f406e1ae..807184fd5618 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -758,6 +758,14 @@ parse_panel_options(struct drm_i915_private *i915,
>  
>  	panel->vbt.lvds_dither = lvds_options->pixel_dither;
>  
> +	/*
> +	 * Empirical evidence indicates the block size can be
> +	 * either 4,14,16,24+ bytes. For older VBTs no clear
> +	 * relationship between the block size vs. BDB version.
> +	 */
> +	if (get_blocksize(lvds_options) < 16)
> +		return;
> +
>  	drrs_mode = (lvds_options->dps_panel_type_bits
>  				>> (panel_type * 2)) & MODE_MASK;
>  	/*

-- 
Jani Nikula, Intel Open Source Graphics Center