linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915: Clear pipe's pll hw state in hsw_dp_set_ddi_pll

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Date:	Wed, 01 Jul 2015 17:54:06 +0300
From:	Ander Conselvan De Oliveira <conselvan2@...il.com>
To:	Jani Nikula <jani.nikula@...ux.intel.com>
Cc:	Daniel Vetter <daniel@...ll.ch>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	DRI mailing list <dri-devel@...ts.freedesktop.org>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Intel-gfx] [PATCH] drm/i915: Clear pipe's pll hw state in
 hsw_dp_set_ddi_pll_sel()

On Tue, 2015-06-30 at 18:41 +0300, Jani Nikula wrote:
> On Tue, 30 Jun 2015, Daniel Vetter <daniel@...ll.ch> wrote:
> > On Tue, Jun 30, 2015 at 04:47:06PM +0300, Jani Nikula wrote:
> >> On Tue, 30 Jun 2015, Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@...el.com> wrote:
> >> > Similarly to what is done for SKL, clear the dpll_hw_state of the pipe
> >> > config in hsw_dp_set_ddi_pll_sel(), since it main contain stale values.
> >> > That can happen if a crtc that was previously driving an HDMI connector
> >> > switches to a DP connector. In that case, the wrpll field was left with
> >> > its old value, leading to warnings like the one below:
> >> >
> >> > [drm:check_crtc_state [i915]] *ERROR* mismatch in dpll_hw_state.wrpll (expected 0xb035061f, found 0x00000000)
> >> > ------------[ cut here ]------------
> >> > WARNING: CPU: 1 PID: 767 at drivers/gpu/drm/i915/intel_display.c:12324 check_crtc_state+0x975/0x10b0 [i915]()
> >> > pipe state doesn't match!
> >> >
> >> > This regression was indroduced in
> >> >
> >> > commit dd3cd74acf12723045a64f1f2c6298ac7b34a5d5
> >> > Author: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@...el.com>
> >> > Date:   Fri May 15 13:34:29 2015 +0300
> >> >
> >> >     drm/i915: Don't overwrite (e)DP PLL selection on SKL
> >> >
> >> > Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@...el.com>
> >> 
> >> Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
> >> Tested-by: Jani Nikula <jani.nikula@...el.com>
> >
> > Yeah makes sense as a fix for 4.2. But for 4.3 I wonder whether the
> > original commit that started this chain needs to be changed a bit:
> >
> > commit 4978cc93d9ac240b435ce60431aef24239b4c270
> > Author: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@...el.com>
> > Date:   Tue Apr 21 17:13:21 2015 +0300
> >
> >     drm/i915: Preserve shared DPLL information in new pipe_config
> >
> > All the trouble this caused is because it not only preserves the sharing
> > config (in crtc_state->shared_dpll) but also the ->dpll_hw_state. And I
> > think with Maarten's latest code (for 4.3) we'd just do an unconditional
> > compute_config (need it for fast pfit updates and fastboot), which means
> > the bogus values in ->dpll_hw_state aren't a problem any more since we'll
> > overwrite them again. And then we could remove that sprinkle of memsets we
> > have all over, which would be good (since the current approach is
> > obviously a bit fragile). Anyway:
> >
> > Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> 
> Pushed to drm-intel-next-fixes, thanks for the patch and review. One
> down, another one left to fix.

I made some progress on the second issue, but I'm afraid Jani might have
a found a third bug. The warning he gets happens because we try to wait
for vblanks while updating the primary plane during the modeset. At that
point, the crtc is off. The problem is in intel_check_primary_plane(),
which is called from drm_atomic_helper_check_planes(). That function
makes decisions about waiting for a vblank based on intel_crtc->active.
Since the check is called before we disable the crtcs, active might be
true, even though the plane update is done with crtcs disable.

The patch below makes the warning go away, but I still need to figure
out how to set crtc_state->planes_changed properly if we are going down
that route.

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index dcb1d25..f14727c 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12480,10 +12480,6 @@ intel_modeset_compute_config(struct drm_crtc *crtc,
 
        intel_dump_pipe_config(to_intel_crtc(crtc), pipe_config,"[modeset]");
 
-       ret = drm_atomic_helper_check_planes(state->dev, state);
-       if (ret)
-               return ERR_PTR(ret);
-
        return pipe_config;
 }
 

The backtrace on Linus' machine is different, though. It comes from the
call to intel_crtc_disable_planes() in __intel_set_mode(). That would
indicate we have a crtc with crtc->state->enable == true but that is
actually inactive. I'm still not sure how we can get in that state.

Ander

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