Re: [Intel-gfx] [PATCH] drm/i915/vbt: update DP max link rate table

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Feb 08, 2021 at 01:31:57PM +0000, Lee, Shawn C wrote:
> On Fri, Feb 05, 2021, at 8:26 p.m, Ville Syrjälä wrote:
> >On Mon, Feb 01, 2021 at 11:02:28PM +0800, Lee Shawn C wrote:
> >> According to Bspec #20124, max link rate table for DP was updated at 
> >> BDB version 230. Max link rate can support upto UHBR.
> >> 
> >> After migrate to BDB v230, the definition for LBR, HBR2 and HBR3 were 
> >> changed. For backward compatibility. If BDB version was from 216 to 
> >> 229. Driver have to follow original rule to configure DP max link rate 
> >> value from VBT.
> >> 
> >> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> >> Cc: Imre Deak <imre.deak@intel.com>
> >> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> >> Cc: Cooper Chiou <cooper.chiou@intel.com>
> >> Cc: William Tseng <william.tseng@intel.com>
> >> Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
> >> ---
> >>  drivers/gpu/drm/i915/display/intel_bios.c     | 24 ++++++++++++++++++-
> >>  drivers/gpu/drm/i915/display/intel_vbt_defs.h | 14 +++++++----
> >>  2 files changed, 32 insertions(+), 6 deletions(-)
> >> 
> >> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c 
> >> b/drivers/gpu/drm/i915/display/intel_bios.c
> >> index 04337ac6f8c4..be1f732e6550 100644
> >> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> >> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> >> @@ -1876,7 +1876,15 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv,
> >>  	/* DP max link rate for CNL+ */
> >>  	if (bdb_version >= 216) {
> >>  		switch (child->dp_max_link_rate) {
> >> -		default:
> >> +		case VBT_DP_MAX_LINK_RATE_UHBR20:
> >> +			info->dp_max_link_rate = 2000000;
> >> +			break;
> >> +		case VBT_DP_MAX_LINK_RATE_UHBR13P5:
> >> +			info->dp_max_link_rate = 1350000;
> >> +			break;
> >> +		case VBT_DP_MAX_LINK_RATE_UHBR10:
> >> +			info->dp_max_link_rate = 1000000;
> >> +			break;
> >>  		case VBT_DP_MAX_LINK_RATE_HBR3:
> >>  			info->dp_max_link_rate = 810000;
> >>  			break;
> >> @@ -1889,7 +1897,21 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv,
> >>  		case VBT_DP_MAX_LINK_RATE_LBR:
> >>  			info->dp_max_link_rate = 162000;
> >>  			break;
> >> +		case VBT_DP_MAX_LINK_RATE_DEFAULT:
> >> +		default:
> >> +			info->dp_max_link_rate = 0;
> >> +			break;
> >> +		}
> >> +
> >> +		if (bdb_version < 230) {
> >> +			if (child->dp_max_link_rate == VBT_DP_MAX_LINK_RATE_DEFAULT)
> >> +				info->dp_max_link_rate = 810000;
> >> +			else if (child->dp_max_link_rate == VBT_DP_MAX_LINK_RATE_LBR)
> >> +				info->dp_max_link_rate = 540000;
> >> +			else if (child->dp_max_link_rate == VBT_DP_MAX_LINK_RATE_HBR2)
> >> +				info->dp_max_link_rate = 162000;
> >>  		}
> >
> >I would split this into two separate functions, one does the new mapping, the other the old mapping. 
> >
> 
> I will split this into two separate functions in patch v2.

Actually looking through the VBT history this seems to have been
retroactively changed for already rev 216+ to follow the new
definitions. And naturally no actual explanation given. So it's
the same old VBT==snafu as always.

I guess the real question is whether any machines migth have shipped
that depened on the old defitions? Unless someone manages to
find that out I think we might just have to change this to follow
only the new style and hope we don't regress a lot of machines.

I was a bit hopeful that this might have fixed [1], but looks
like that just has this set to 0 which doesn't give us the desired
2.7Gbps with either the old or new definition :(

[1] https://gitlab.freedesktop.org/drm/intel/-/issues/3034

-- 
Ville Syrjälä
Intel
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