On Tue, Nov 14, 2023 at 03:07:52PM +0200, Imre Deak wrote:
> On Tue, Nov 14, 2023 at 11:00:49AM +0200, Jani Nikula wrote:
> > On Mon, 13 Nov 2023, Imre Deak <imre.deak@xxxxxxxxx> wrote:
> > > Apply the correct BW allocation overhead and channel coding efficiency
> > > on UHBR link rates, similarly to DP1.4 link rates.
> > >
> > > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
> > > ---
> > > drivers/gpu/drm/i915/display/intel_display.c | 10 ----------
> > > 1 file changed, 10 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> > > index 3effafcbb411a..24aebdb715e7d 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > > @@ -2398,16 +2398,6 @@ add_bw_alloc_overhead(int link_clock, int bw_overhead,
> > > int ch_coding_efficiency =
> > > drm_dp_bw_channel_coding_efficiency(is_uhbr);
> >
> > Why do we have this and intel_dp_max_data_rate() separately?
>
> This function calculates an m/n ratio for a given pixel/data rate,
> applying both the allocation overhead (FEC, SSC, etc.) and the channel
> coding efficiency. intel_dp_max_data_rate() calculates a maximum data
> rate applying only the channel coding efficiency.
>
> I think intel_dp_max_data_rate() could be simplified, so the two
> functions use the same channel coding efficiency to:
>
> DIV_ROUND_UP_ULL(mul_u32_u32(max_link_rate_kbps * max_lanes,
> drm_dp_bw_channel_coding_efficiency(is_uhbr)),
> 1000000ULL * 8)
Actually, it does make sense to reuse intel_dp_max_data_rate() in
intel_link_compute_m_n() -> add_bw_alloc_overhead(), I'll send a new
version with that (and the above simplification).
>
> --Imre
>
> >
> > BR,
> > Jani.
> >
> >
> > >
> > > - /*
> > > - * TODO: adjust for actual UHBR channel coding efficiency and BW
> > > - * overhead.
> > > - */
> > > - if (is_uhbr) {
> > > - *data_m = pixel_data_rate;
> > > - *data_n = link_data_rate * 8 / 10;
> > > - return;
> > > - }
> > > -
> > > *data_m = DIV_ROUND_UP_ULL(mul_u32_u32(pixel_data_rate, bw_overhead),
> > > 1000000);
> > > *data_n = DIV_ROUND_DOWN_ULL(mul_u32_u32(link_data_rate, ch_coding_efficiency),
> >
> > --
> > Jani Nikula, Intel
