Message-ID: <20180409082337.GG31310@phenom.ffwll.local>
Date:   Mon, 9 Apr 2018 10:23:37 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Ayan Halder <ayan.halder@....com>
Cc:     Daniel Vetter <daniel@...ll.ch>, Liviu Dudau <liviu.dudau@....com>,
        Brian Starkey <brian.starkey@....com>,
        Mali DP Maintainers <malidp@...s.arm.com>,
        Dave Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        nd <nd@....com>
Subject: Re: [PATCH 8/8] drm/arm/malidp: Added the late system pm functions

On Fri, Apr 06, 2018 at 08:02:16PM +0100, Ayan Halder wrote:
> 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@....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@....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.

This article is from 2012. That's not really recommended best practices
anymore. device_links have only been added a few years ago, so ofc an
article from 2012 can't tell you that you should use those instead :-)

That's why I brought this up, we have much better ways to handle device
dependencies now.

Also, you still haven't explained what exactly the dependency is.
-Daniel

> 
> > >> > ---
> > >> >  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@...ts.freedesktop.org
> > >> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> > >>
> > >> --
> > >> Daniel Vetter
> > >> Software Engineer, Intel Corporation
> > >> http://blog.ffwll.ch
> > >> _______________________________________________
> > >> dri-devel mailing list
> > >> dri-devel@...ts.freedesktop.org
> > >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
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> > 
> > 
> > 
> > -- 
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > +41 (0) 79 365 57 48 - http://blog.ffwll.ch

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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