Re: [Freedreno] [PATCH 2/2] drm/msm: Add MSM_WAIT_IOVA ioctl

[Rob Clark]

On Mon, Jan 13, 2020 at 9:51 AM Jordan Crouse <jcrouse@xxxxxxxxxxxxxx> wrote:
>
> On Mon, Jan 13, 2020 at 10:36:05AM -0500, Brian Ho wrote:
> > +
> > +     vaddr = base_vaddr + args->offset;
> > +
> > +     /* Assumes WC mapping */
> > +     ret = wait_event_interruptible_timeout(
> > +                     gpu->event, *vaddr >= args->value, remaining_jiffies);
>
> I feel like a barrier might be needed before checking *vaddr just in case you
> get the interrupt and wake up the queue before the write posts from the
> hardware.
>

if the gpu is doing posted (or cached) writes, I don't think there is
even a CPU side barrier primitive that could wait for that?  I think
we rely on the GPU not interrupting the CPU until the write is posted

BR,
-R