[Intel-gfx] [PATCH 11/15] drm/i915: Nuke intel_bw_calc_min_cdclk()

[Ville Syrjälä]

On Tue, Feb 01, 2022 at 01:18:18PM +0200, Lisovskiy, Stanislav wrote:
> On Tue, Feb 01, 2022 at 12:05:13PM +0200, Ville Syrjälä wrote:
> > On Tue, Feb 01, 2022 at 10:52:39AM +0200, Lisovskiy, Stanislav wrote:
> > > On Tue, Jan 18, 2022 at 11:23:50AM +0200, Ville Syrjala wrote:
> > > > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > > 
> > > > intel_bw_calc_min_cdclk() is entirely pointless. All it manages to do is
> > > > somehow conflate the per-pipe min cdclk with dbuf min cdclk. There is no
> > > > (at least documented) dbuf min cdclk limit on pre-skl so let's just get
> > > > rid of all this confusion.
> > > > 
> > > > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > 
> > > I think we constantly have a bit contradictional attitude towards such situation.
> > > >From one perspective you can say, that those kind of "leagcy" callbacks are
> > > pointless, from the other hand one might say. that we need to have a unified
> > > approach for all platforms and I think we got, some legacy handlers for old
> > > platforms for similar purpose as well.
> > > I'm fine with both approaches, however for example when I was submitting
> > > that patch, I was asked by reviewer to add this kind of legacy callback, so that we have
> > > a "uniform" approach.
> > > We just then need to have some standard agreement on those, which doesn't
> > > depend on today's cosmic radiation levels :)
> > 
> > Yes in general I prefer a unified approach across all platforms.
> > But in this case there is nothing to do for the old platforms as they
> > don't have any kind of dbuf cdclk limit, or if there is one we don't
> > know what it is since it's not documented.
> > 
> > So the only thing the code was really doing was conflating the
> > per-pipe cdclk limit (which is handled elsewhere for all platforms
> > in a  unified fashion) with something that doesn't even exist.
> > 
> > Also I don't think it was even correct anyway since it was
> > using the per-pipe cdclk_state->min_cdclk[] already during
> > intel_cdclk_atomic_check(), but cdclk_state->min_cdclk[]
> > isn't even computed until intel_modeset_calc_cdclk() which 
> > is called later. So I guess it was basically just computing 
> > the max of the min_cdclk[] for all the pipes for the _old_
> > state, not the new state.
> 
> No, I think actually the idea was that it was first calculating
> new_bw_state->min_cdclk, based on plane and dbuf bandwidth requirements
> in intel_atomic_check_cdclk,

Well intel_bw_calc_min_cdclk() did none of that. Like I said it
just took the max of the _old_ per-pipe cdclk_state->min_cdclk[]
values and stored that as the *new* bw min cdclk, which later
would get consulted by intel_compute_min_cdclk().

-- 
Ville Syrjälä
Intel