Re: [PATCH v2 1/1] drm/i915: Use the correct max source link rate for MST

[Lyude Paul <lyude@redhat.com>]

Alright - I had Ville double check this and give their A-B on IRC (I just need
to fix the open coded link_rate_to_bw() here). Since this got broken on drm-
misc-next I'm going to go ahead and push the fix there, since I'm not going to
be around next Monday or Tuesday and I don't want to leave i915 broken in the
interim. Sorry about the noise with this Jani!

As well - I'll get to fixing the dpcd unit usage once I get back on Wednesday
(unless Nikola's already gotten to it by then) so we use KHz instead. Although
as ville has pointed out, I think we should teach the topology manager to allow
passing for the current link rate/lane count during state computation in the
long term.

On Fri, 2021-04-30 at 17:45 -0400, Nikola Cornij wrote:
> [why]
> Previously used value was not safe to provide the correct value, i.e. it
> could be 0 if not not configured, leading to no MST on this platform.
> 
> [how]
> Do not use the value from BIOS, but from the structure populated at
> encoder initialization time.
> 
> Fixes: 98025a62cb00 ("drm/dp_mst: Use Extended Base Receiver Capability DPCD
> space")
> Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
> Reviewed-by: Lyude Paul <lyude@redhat.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index bf7f8487945c..3642d7578658 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -942,7 +942,7 @@ intel_dp_mst_encoder_init(struct intel_digital_port
> *dig_port, int conn_base_id)
>         struct intel_dp *intel_dp = &dig_port->dp;
>         enum port port = dig_port->base.port;
>         int ret;
> -       int bios_max_link_rate;
> +       int max_source_rate = intel_dp->source_rates[intel_dp-
> >num_source_rates - 1];
>  
>         if (!HAS_DP_MST(i915) || intel_dp_is_edp(intel_dp))
>                 return 0;
> @@ -957,11 +957,11 @@ intel_dp_mst_encoder_init(struct intel_digital_port
> *dig_port, int conn_base_id)
>  
>         /* create encoders */
>         intel_dp_create_fake_mst_encoders(dig_port);
> -       bios_max_link_rate = intel_bios_dp_max_link_rate(&dig_port->base);
>         ret = drm_dp_mst_topology_mgr_init(&intel_dp->mst_mgr, &i915->drm,
>                                            &intel_dp->aux, 16, 3,
>                                            (u8)dig_port->max_lanes,
> -                                          (u8)(bios_max_link_rate / 27000),
> conn_base_id);
> +                                          (u8)(max_source_rate / 27000),
> +                                          conn_base_id);
>         if (ret)
>                 return ret;
>  

-- 
Sincerely,
   Lyude Paul (she/her)
   Software Engineer at Red Hat
   
Note: I deal with a lot of emails and have a lot of bugs on my plate. If you've
asked me a question, are waiting for a review/merge on a patch, etc. and I
haven't responded in a while, please feel free to send me another email to check
on my status. I don't bite!

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