Re: [PATCH 8/8] drm/arm/malidp: Added the late system pm functions

From: Ayan Halder <ayan.halder@arm.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Liviu Dudau <liviu.dudau@arm.com>,
	Brian Starkey <brian.starkey@arm.com>,
	Mali DP Maintainers <malidp@foss.arm.com>,
	Dave Airlie <airlied@linux.ie>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	nd <nd@arm.com>
Subject: Re: [PATCH 8/8] drm/arm/malidp: Added the late system pm functions
Date: Fri, 6 Apr 2018 20:02:16 +0100	[thread overview]
Message-ID: <20180406190216.GA18433@arm.com> (raw)
In-Reply-To: <CAKMK7uF8mmLOBQtwfQgkdpPHfoy7yM9UApWgc9YiEudoP5WEyw@mail.gmail.com>

On Tue, Mar 27, 2018 at 01:09:36PM +0200, Daniel Vetter wrote:
> On Tue, Mar 27, 2018 at 11:59 AM, Ayan Halder <ayan.halder@arm.com> wrote:
> > On Tue, Mar 27, 2018 at 10:29:03AM +0200, Daniel Vetter wrote:
> >> On Mon, Mar 26, 2018 at 06:03:20PM +0100, Ayan Kumar Halder wrote:
> >> > malidp_pm_suspend_late checks if the runtime status is not suspended
> >> > and if so, invokes malidp_runtime_pm_suspend which disables the
> >> > display engine/core interrupts and the clocks. It sets the runtime status
> >> > as suspended. Subsequently, malidp_pm_resume_early will invoke
> >> > malidp_runtime_pm_resume which enables the clocks and the interrupts
> >> > (previously disabled) and sets the runtime status as active.
> >> >
> >> > Signed-off-by: Ayan Kumar Halder <ayan.halder@arm.com>
> >> > Change-Id: I5f8c3d28f076314a1c9da2a46760a9c37039ccda
> >>
> >> Why exactly do you need late/early hooks? If you have dependencies with
> >> other devices, pls consider adding device_links instead. This here
> >> shouldn't be necessary.
> >> -Daniel
> > We need to late/early hooks to disable malidp interrupts and the
> > clocks.
> 
> Yes, but why this ordering constraint? Why can't you just disable the
> interrupts/clocks in the normal suspend code. I see that the patch
> does this, I want to understand why it does it.
> -Daniel
Apologies for my delayed response on this. 

With reference to https://lwn.net/Articles/505683/ :-
1. "suspend() should leave the device in a quiescent state." We invoke
drm_mode_config_helper_suspend() which deactivates the crtc. I
understand that this is the quiescent state.

2. "suspend_late() can often be the same as runtime_suspend()."  We
invoke runtime suspend/resume calls in late/early hooks.

> >> > ---
> >> >  drivers/gpu/drm/arm/malidp_drv.c | 17 +++++++++++++++++
> >> >  1 file changed, 17 insertions(+)
> >> >
> >> > diff --git a/drivers/gpu/drm/arm/malidp_drv.c b/drivers/gpu/drm/arm/malidp_drv.c
> >> > index bd44a6d..f6124d8 100644
> >> > --- a/drivers/gpu/drm/arm/malidp_drv.c
> >> > +++ b/drivers/gpu/drm/arm/malidp_drv.c
> >> > @@ -766,8 +766,25 @@ static int __maybe_unused malidp_pm_resume(struct device *dev)
> >> >     return 0;
> >> >  }
> >> >
> >> > +static int __maybe_unused malidp_pm_suspend_late(struct device *dev)
> >> > +{
> >> > +   if (!pm_runtime_status_suspended(dev)) {
> >> > +           malidp_runtime_pm_suspend(dev);
> >> > +           pm_runtime_set_suspended(dev);
> >> > +   }
> >> > +   return 0;
> >> > +}
> >> > +
> >> > +static int __maybe_unused malidp_pm_resume_early(struct device *dev)
> >> > +{
> >> > +   malidp_runtime_pm_resume(dev);
> >> > +   pm_runtime_set_active(dev);
> >> > +   return 0;
> >> > +}
> >> > +
> >> >  static const struct dev_pm_ops malidp_pm_ops = {
> >> >     SET_SYSTEM_SLEEP_PM_OPS(malidp_pm_suspend, malidp_pm_resume) \
> >> > +   SET_LATE_SYSTEM_SLEEP_PM_OPS(malidp_pm_suspend_late, malidp_pm_resume_early) \
> >> >     SET_RUNTIME_PM_OPS(malidp_runtime_pm_suspend, malidp_runtime_pm_resume, NULL)
> >> >  };
> >> >
> >> > --
> >> > 2.7.4
> >> >
> >> > _______________________________________________
> >> > dri-devel mailing list
> >> > dri-devel@lists.freedesktop.org
> >> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >>
> >> --
> >> Daniel Vetter
> >> Software Engineer, Intel Corporation
> >> http://blog.ffwll.ch
> >> _______________________________________________
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> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch