[Intel-gfx] [PATCH] drm/i915: Reset dpll_hw_state when selecting a new pll on hsw

[Jani Nikula]

On Wed, 14 Oct 2015, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Wed, Oct 14, 2015 at 04:58:55PM +0300, Ander Conselvan De Oliveira wrote:
>> On Wed, 2015-10-14 at 14:44 +0200, Daniel Vetter wrote:
>> > On Wed, Oct 14, 2015 at 11:21:46AM +0300, Ander Conselvan De Oliveira wrote:
>> > > On Tue, 2015-10-13 at 16:08 +0200, Daniel Vetter wrote:
>> > > > On Tue, Oct 13, 2015 at 04:00:37PM +0200, Maarten Lankhorst wrote:
>> > > > > Op 13-10-15 om 15:58 schreef Daniel Vetter:
>> > > > > > On Tue, Oct 13, 2015 at 03:43:28PM +0200, Maarten Lankhorst wrote:
>> > > > > > > Op 13-10-15 om 15:35 schreef Daniel Vetter:
>> > > > > > > > On Tue, Oct 13, 2015 at 03:18:16PM +0200, Maarten Lankhorst wrote:
>> > > > > > > > > Op 23-09-15 om 17:34 schreef Gabriel Feceoru:
>> > > > > > > > > > Using 2 connectors (DVI and VGA) will cause wrpll to be set for
>> > > > > > > > > > INTEL_OUTPUT_HDMI but never reset if switching to INTEL_OUTPUT_VGA
>> > > > > > > > > > 
>> > > > > > > > > > Supresses errors like these:
>> > > > > > > > > > [drm:intel_pipe_config_compare [i915]] *ERROR* mismatch in dpll_hw_state.wrpll
>> > > > > > > > > > 
>> > > > > > > > > Looks like a good idea to always zero it.
>> > > > > > > > Except that we still have a bunch of cases where we recompute clock state
>> > > > > > > > but only partially. Can we just move them all up into a common place
>> > > > > > > > please? That would also catch cases where we simply forget to fill this
>> > > > > > > > out at all.
>> > > > > > > > 
>> > > > > > > > One case I noticed is edp in skl_ddi_pll_select, but there's probably
>> > > > > > > > more.
>> > > > > > > > 
>> > > > > > > Something like below, with all the memsets for dpll_hw_state removed?
>> > > > > > I think this will blow up since we recompute clock state only when
>> > > > > > needs_modeset is true. So needs a bit more intelligence in deciding when
>> > > > > > to clear it I think.
>> > > > > Oops you're right. Maybe intel_modeset_clear_plls because that's where all the clock state
>> > > > > belongs?
>> > > > 
>> > > > Yeah that might be an even better place, in the loop after the continue;
>> > > > statement.
>> > > 
>> > > The reason I didn't put the memset there in the first place was the way we calculate plls for DP
>> > > with DDI platforms. In that case, ddi_pll_sel is setup from the encoder_config instead of
>> > > compute_clock, so a memset ends up clearing the new pll config.
>> > 
>> > Hm, I forgot about this split totally. And there seems to be a giant mess
>> > going on here:
>> > 
>> > In our top-level intel_atomic_check we have 4 parts to compute state:
>> > 1. drm_atomic_helper_check_modeset
>> > 2. intel_modeset_pipe_config
>> > 3. intel_modeset_checks
>> > 4. drm_atomic_helper_check_planes
>> > 
>> > We recalculate clocks (by calling dev_priv->display.crtc_compute_clock)
>> > in 1., way ahead of anything else in intel_crtc_atomic_check. That looks
>> > very suspcious since it means only very later on (in the loop that does
>> > 2.) do we even decide whether we need to do a full modeset or not.
>> > 
>> > So what I had in mind is that we clear clocks in
>> > intel_modeset_pipe_config, before we call any of the callbacks. That makes
>> > sure that when we decided to do a modeset, we do recompute the clocks
>> > correctly.
>> 
>> I had a suspicion this would interact badly with how we "cancel" the modeset if the pipe config
>> didn't changed, just after the call to intel_modeset_pipe_config(). It turns out there's an issue
>> there already.
>> 
>> There are two possibilities for the dpll_hw_state value after the new pipe_config is calculated. It
>> may have the new values already for DP in HSW/BDW and eDP in SKL or it may still have the old value.
>> In the latter case the new value is only calculated in .crtc_clock(), after we already compared the
>> old and new configs and may have decided to skip the modeset.
>> 
>> But doing the memset() in intel_modeset_pipe_config() would be find as long as we don't change our
>> minds about doing a modeset later.
>
> It's more annoying since my analysis is all wrong: intel_crtc_atomic_check
> is called from drm_atomic_helper_check_planes, i.e. step 4 not step 1.
> It'll all work out I think if we memset it in intel_modeset_pipe_config.
> The caveat is that we need to move the clock recomputation into
> intel_modeset_pipe_config too (which is better, since then we'll have more
> accurate state to decided whether we'll fastboot or not).
>
> And then intel_modeset_clear_plls would really just update the global pll
> setup (and would be really good to rename it to
> intel_modeset_compute_shared_dpll or whatever).
>
> Thoughts?

Ander, Maarten, where are we with this? Is it horribly wrong to merge
the original patch in this ever-growing and diverging thread?

BR,
Jani.




-- 
Jani Nikula, Intel Open Source Technology Center