[Intel-gfx] [PATCH 3/5] drm/i915: Enable vblanks after verifying power domain states.

[Rodrigo Vivi]

On Fri, Jan 05, 2018 at 11:23:54AM +0000, Maarten Lankhorst wrote:
> Op 04-01-18 om 22:51 schreef Pandiyan, Dhinakaran:
> > On Thu, 2018-01-04 at 12:35 +0100, Maarten Lankhorst wrote:
> >> Wouldn't it be better to make intel_power_domains_verify_state work
> >> correctly with the vblank irq?
> > I tried to :) Since I changed the domain_use_count to atomic_t and moved
> > it outside of the locks, verify_state became racy. Let me take another
> > look.
> >
> > -DK
> 
> It sucks that we end up with 2 ways to handle power domains..

I also don't like that, but if we need to go with that I believe
we need to go with a generic approach.

> 
> I'm trying to think of a cleaner way, coming up with none. :(

me neither :(

> 
> It would have been nice if we could do something like a seqlock for
> the refcounts, but that would prevent us from blocking too..

reader does't block and writer doesn't wait for the reader so not
sure we could use this.

> 
> Is it only the DC off power well we care about?

It is the only call to any power well that comes from an spin-locked
region. So we can't sleep.

I think we looked to the option of changing the entire pw to spin locks
instead of mutexs, but we concluded it wasn't a viable option as well.
I just can't remember why right now.

Thanks,
Rodrigo.

> 
> ~Maarten
>