[Intel-gfx] [Intel-xe] [PATCH] drm/i915: don't use uncore spinlock to protect critical section in vblank

[Coelho, Luciano]

On Fri, 2023-11-17 at 10:41 +0200, Ville Syrjälä wrote:
> On Fri, Nov 17, 2023 at 08:05:21AM +0000, Coelho, Luciano wrote:
> > Thanks for your comments, Ville!
> > 
> > On Fri, 2023-11-17 at 09:19 +0200, Ville Syrjälä wrote:
> > > On Thu, Nov 16, 2023 at 01:27:00PM +0200, Luca Coelho wrote:
> > > > Since we're abstracting the display code from the underlying driver
> > > > (i.e. i915 vs xe), we can't use the uncore's spinlock to protect
> > > > critical sections of our code.
> > > > 
> > > > After further inspection, it seems that the spinlock is not needed at
> > > > all and this can be handled by disabling preemption and interrupts
> > > > instead.
> > > 
> > > uncore.lock has multiple purposes:
> > > 1. serialize all register accesses to the same cacheline as on
> > >    certain platforms that can hang the machine
> > 
> > Okay, do you remember which platforms?
> 
> HSW is the one I remember for sure being affected.
> Althoguh I don't recall if I ever managed to hang it
> using display registers specifically. intel_gpu_top
> certainly was very good at reproducing the problem.

So do we know if the display registers are affected at all?


> > I couldn't find any reference to
> > this reason. 
> 
> If all else fails git log is your friend.

Of course! That's where I found the info about the RT stuff.  But I
didn't find anything else regarding this.  Maybe I should just look
harder, if you don't have a reference at hand. ;)

--
Cheers,
Luca.