Messages in this thread | | | From | Clément Péron <> | Date | Fri, 29 May 2020 14:35:08 +0200 | Subject | Re: [PATCH 05/15] drm/panfrost: use spinlock instead of atomic |
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Hi Robin,
On Fri, 29 May 2020 at 14:20, Robin Murphy <robin.murphy@arm.com> wrote: > > On 2020-05-10 17:55, Clément Péron wrote: > > Convert busy_count to a simple int protected by spinlock. > > A little more reasoning might be nice.
I have follow the modification requested for lima devfreq and clearly don't have any argument to switch to spinlock.
The Lima Maintainer asked to change witht the following reason : "Better make this count a normal int which is also protected by the spinlock, because current implementation can't protect atomic ops for state change and busy idle check and we are using spinlock already"
> > > Signed-off-by: Clément Péron <peron.clem@gmail.com> > > --- > [...] > > diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.h b/drivers/gpu/drm/panfrost/panfrost_devfreq.h > > index 0697f8d5aa34..e6629900a618 100644 > > --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.h > > +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.h > > @@ -4,6 +4,7 @@ > > #ifndef __PANFROST_DEVFREQ_H__ > > #define __PANFROST_DEVFREQ_H__ > > > > +#include <linux/spinlock.h> > > #include <linux/ktime.h> > > > > struct devfreq; > > @@ -14,10 +15,17 @@ struct panfrost_device; > > struct panfrost_devfreq { > > struct devfreq *devfreq; > > struct thermal_cooling_device *cooling; > > + > > ktime_t busy_time; > > ktime_t idle_time; > > ktime_t time_last_update; > > - atomic_t busy_count; > > + int busy_count; > > + /* > > + * Protect busy_time, idle_time, time_last_update and busy_count > > + * because these can be updated concurrently, for example by the GP > > + * and PP interrupts. > > + */ > > Nit: this comment is clearly wrong, since we only have Job, GPU and MMU > interrupts here. I guess if there is a race it would be between > submission/completion/timeout on different job slots.
It's copy/paste from lima I will update it,
> > Given that, should this actually be considered a fix for 9e62b885f715 > ("drm/panfrost: Simplify devfreq utilisation tracking")?
I can't say if it can be considered as a fix, I didn't see any improvement on my board before and after this patch. I'm still facing some issue and didn't have time to fully investigate it.
Thanks for you review,
> > Robin.
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