Re: [PATCH 8/8] drm/arm/malidp: Added the late system pm functions
From: Brian Starkey
Date: Mon Apr 09 2018 - 12:15:21 EST
Hi Daniel,
On Mon, Apr 09, 2018 at 10:23:37AM +0200, Daniel Vetter wrote:
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@xxxxxxx> 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@xxxxxxx>
> >> > 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.
We aren't trying to manage any device dependencies here, I don't know
where that idea came from?
The kernel-doc on drm-next this afternoon says effectively the same
thing:
* @suspend: Executed before putting the system into a sleep state in which the
* contents of main memory are preserved. The exact action to perform
* depends on the device's subsystem (PM domain, device type, class or bus
* type), but generally the device must be quiescent after subsystem-level
* @suspend() has returned, so that it doesn't do any I/O or DMA.
* Subsystem-level @suspend() is executed for all devices after invoking
* subsystem-level @prepare() for all of them.
(i.e. suspend() makes the device quiescent).
* @suspend_late: Continue operations started by @suspend(). For a number of
* devices @suspend_late() may point to the same callback routine as the
* runtime suspend callback.
(suggests suspend_late() be assigned to the same function as runtime
suspend).
As for why, my understanding is like so:
For ->suspend(), we use the DRM helper, which disables the CRTC.
Normally disabling the CRTC would be enough to also invoke our
pm_runtime callback to do the final clock disable etc., however when a
system suspend is in-progress, the core forcibly takes a runtime
reference on all devices - preventing any pm_runtime paths from
running.
This means that after the CRTC is disabled in ->suspend(), our normal
pm_runtime path will not be invoked, and so the things done in
malidp_runtime_pm_suspend() will never happen.
We were just following the advice in the kernel-doc to deal with this.
The alternative would be to call malidp_runtime_pm_{suspend,resume}
from the "not late" hooks, but I'd ask why?
Also, you still haven't explained what exactly the dependency is.
Because there isn't one :-)
Thanks,
-Brian
-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
> >> >
> >> > _______________________________________________
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> >>
> >> --
> >> 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
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch