On Sat, Feb 03, 2024 at 10:25:18AM -0300, Gustavo Sousa wrote:
> Quoting Ville Syrjälä (2024-02-02 16:58:37-03:00)
> >On Fri, Feb 02, 2024 at 10:12:08AM -0300, Gustavo Sousa wrote:
> >> Looks like the name and description of intel_cdclk_needs_modeset()
> >> became inacurate as of commit 59f9e9cab3a1 ("drm/i915: Skip modeset for
> >> cdclk changes if possible"), when it became possible to update the cdclk
> >> without requiring disabling the pipes when only changing the cd2x
> >> divider was enough.
> >>
> >> Later on we also added the same type of support with squash and crawling
> >> with commit 25e0e5ae5610 ("drm/i915/display: Do both crawl and squash
> >> when changing cdclk"), commit d4a23930490d ("drm/i915: Allow cdclk
> >> squasher to be reconfigured live") and commit d62686ba3b54
> >> ("drm/i915/adl_p: CDCLK crawl support for ADL").
> >>
> >> As such, update that function's name and documentation to something more
> >> appropriate, since the real checks for requiring modeset are done
> >> elsewhere.
> >>
> >> Signed-off-by: Gustavo Sousa <gustavo.sousa@xxxxxxxxx>
> >> ---
> >>
> >> One thing worth noting here is that, with this change, we are left with an
> >> awkward situation where two function names related to checking changes in cdclk:
> >>
> >> intel_cdclk_params_changed() and intel_cdclk_changed()
> >>
> >> ,
> >>
> >> and I find it weird that we have intel_cdclk_changed(), which checks for the
> >> voltage level as well. Shouldn't the voltage level be a function of cdclk and
> >> ddi clock? Why do we need that?
> >>
> >> drivers/gpu/drm/i915/display/intel_cdclk.c | 15 +++++++--------
> >> drivers/gpu/drm/i915/display/intel_cdclk.h | 4 ++--
> >> .../drm/i915/display/intel_display_power_well.c | 4 ++--
> >> 3 files changed, 11 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
> >> index 26200ee3e23f..caadd880865f 100644
> >> --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> >> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> >> @@ -2233,17 +2233,16 @@ static bool intel_cdclk_can_squash(struct drm_i915_private *dev_priv,
> >> }
> >>
> >> /**
> >> - * intel_cdclk_needs_modeset - Determine if changong between the CDCLK
> >> - * configurations requires a modeset on all pipes
> >> + * intel_cdclk_params_changed - Check whether CDCLK parameters changed
> >> * @a: first CDCLK configuration
> >> * @b: second CDCLK configuration
> >> *
> >> * Returns:
> >> - * True if changing between the two CDCLK configurations
> >> - * requires all pipes to be off, false if not.
> >> + * True if parameters changed in a way that requires programming the CDCLK
> >> + * and False otherwise.
> >> */
> >> -bool intel_cdclk_needs_modeset(const struct intel_cdclk_config *a,
> >> - const struct intel_cdclk_config *b)
> >> +bool intel_cdclk_params_changed(const struct intel_cdclk_config *a,
> >> + const struct intel_cdclk_config *b)
> >
> >The new name isn't very descriptive either.
>
> Yeah... I would much rather use intel_cdclk_changed(), but that one is
> already taken.
>
> >
> >Outside the cd2x/crawl/squash cases we stil have to consider
> >two cases:
> >1. cdclk frequency/pll changes (voltage level can change or not)
> >2. cdclk frequency/pll doesn't change, but voltage level needs to change
> >
> >And that difference is what intel_cdclk_needs_modeset() is trying
> >convey. And intel_cdclk_changed() tells us whether anything at all
> >is changing.
>
> I might be missing something, but, by going through the specs, it looked
> to me that voltage level was dependent on cdclk (as well as on ddi
> clock) and not the other way around. That's why I find it odd that we
> need an intel_cdclk_changed() that, besides looking for changes in
> cdclk, also checks for the voltage level.
>
> In intel_set_cdclk(), we check intel_cdclk_changed() before continuing.
> If, for example, there is a change in ddi clock that requires a change
> in voltage level but no changes in cdclk, intel_cdclk_changed() would
> return true, right? Wouldn't that make us unnecessarily go through
> intel_set_cdclk()?
intel_set_cdclk() is the thing that does the voltage change.
--
Ville Syrjälä
Intel
