Re: [PATCH] drm/atomic: Add the crtc to affected crtc only if uapi.enable = true

From: "Navare, Manasi" <manasi.d.navare@intel.com>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Daniel Stone <daniels@collabora.com>
Subject: Re: [PATCH] drm/atomic: Add the crtc to affected crtc only if uapi.enable = true
Date: Thu, 1 Apr 2021 14:49:13 -0700	[thread overview]
Message-ID: <20210401214908.GA24310@labuser-Z97X-UD5H> (raw)
In-Reply-To: <YF4ImoReniVIz+TT@intel.com>

On Fri, Mar 26, 2021 at 06:15:22PM +0200, Ville Syrjälä wrote:
> On Thu, Mar 25, 2021 at 03:01:29PM -0700, Navare, Manasi wrote:
> > On Fri, Mar 19, 2021 at 11:27:59PM +0200, Ville Syrjälä wrote:
> > > On Fri, Mar 19, 2021 at 02:26:24PM -0700, Navare, Manasi wrote:
> > > > On Fri, Mar 19, 2021 at 11:12:41PM +0200, Ville Syrjälä wrote:
> > > > > On Fri, Mar 19, 2021 at 01:54:13PM -0700, Navare, Manasi wrote:
> > > > > > On Fri, Mar 19, 2021 at 04:56:24PM +0200, Ville Syrjälä wrote:
> > > > > > > On Thu, Mar 18, 2021 at 04:01:26PM -0700, Navare, Manasi wrote:
> > > > > > > > So basically we see this warning only in case of bigjoiner when
> > > > > > > > drm_atomic_check gets called without setting the state->allow_modeset flag.
> > > > > > > 
> > > > > > > Considering the code is 'WARN(!state->allow_modeset, ...' that
> > > > > > > fact should be rather obvious.
> > > > > > > 
> > > > > > > > 
> > > > > > > > So do you think that in i915, in intel_atomic_check_bigjoiner() we should only
> > > > > > > > steal the crtc when allow_modeset flag is set in state?
> > > > > > > 
> > > > > > > No. If you fully read drm_atomic_check_only() you will observe
> > > > > > > that it will reject any commit w/ allow_modeset==false which 
> > > > > > > needs a modeset. And it does that before the WARN.
> > > > > > > 
> > > > > > > So you're barking up the wrong tree here. The problem I think
> > > > > > > is that you're just computing requested_crtcs wrong.
> > > > > > 
> > > > > > So here in this case, requested CRTC = 0x1 since it requests modeset on CRTC 0
> > > > > > Now in teh atomic check, it steals the slave CRTC 1 and hence affected CRTC comes out
> > > > > > as 0x3 and hence the mismatch.
> > > > > 
> > > > > Hmm. How can it be 0x3 if we filtered out the uapi.enable==false case?
> > > > > 
> > > > 
> > > > Yes if I add that condition like in this patch then it correctly calculates
> > > > the affected crtc bitmask as only 0x1 since it doesnt include the slave crtc.
> > > > So with this patch, requested crtc = 0x 1, affected crtc = 0x1
> > > > 
> > > > If this looks good then this fixes our bigjoiner warnings.
> > > > Does this patch look good to you as is then?
> > > 
> > > I think you still need to fix the requested_crtcs calculation.
> > 
> > We calculate requested crtc at the beginning :
> > for_each_new_crtc_in_state(state, crtc, new_crtc_state, i)
> >                 requested_crtc |= drm_crtc_mask(crtc);
> > 
> > Are you suggesting adding this to after:
> >  if (config->funcs->atomic_check) {
> >                 ret = config->funcs->atomic_check(state->dev, state);
> > 
> >                 if (ret) {
> >                         DRM_DEBUG_ATOMIC("atomic driver check for %p failed: %d\n",
> >                                          state, ret);
> >                         return ret;
> >                 }
> > 		requested_crtc |= drm_crtc_mask(crtc);    // Here it will have requested crtc = 0x11
> >         }
> > 
> > in this case here the state should already have master crtc 0 and slave crtc 1
> > and that requested crtc should already be 0x11
> > 
> > Then in that case we dont need any special check for calculating affected crtc, that also will be 0x11
> 
> All I'm saying is that you're currently calculating requested_crtcs and
> affected_crtcs differently. So I'm not at all surprised that they might
> not match.
>

I dont get your point yet.
requested crtc is calculated before the atomic check call and we dont check for crtc uapi.enable to be true.
And hence requested crtc  = CRTC 0 = 0x2
After I added the check in this patch where affected crtc will include only the crtcs that have uapi.enable = true
then  it perfectly matches the requested crtc and return 0x2 but without this check when the calculation of
requested and affected crtc is the same is where we see the affected crtc = CRTC 0 and 1 = 0x3

So when the calculation is different infcat we dont see the mismatch

What is your point here?

Manasi
> -- 
> Ville Syrjälä
> Intel
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