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

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

On Thu, Feb 11, 2021 at 05:22:05AM +0000, Lee, Shawn C wrote:
> 
> On Wed, Feb 10, 2021 at 04:51 p.m, Ville Syrjälä wrote:
> >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.
> >
> 
> Agree that we should just have the change follow new definition.
> But as you mentioned, we are not sure any machines have shipped
> with the old definition. :(
> 
> In my opinion, we should follow the new style. If we got bug report,
> then we can consider to add some codes for backward compatible.

I went trawling in some really dark waters and found out that
Windows seems to do what you did originally, ie. use the
old definition for 216+, and the new definition for 230+.
So we should just do the same.

-- 
Ville Syrjälä
Intel
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