[PATCH] drm/amdgpu: fix the ib test hang when gfx is in "idle" state

[Huang Rui]

On Mon, Apr 23, 2018 at 10:40:20PM +0800, Alex Deucher wrote:
> On Mon, Apr 23, 2018 at 8:13 AM, Huang Rui <ray.huang at amd.com> wrote:
> > On Mon, Apr 23, 2018 at 05:57:06PM +0800, Koenig, Christian wrote:
> >> Hi Ray,
> >>
> >> Am 23.04.2018 11:47 schrieb Huang Rui <ray.huang at amd.com>:
> >>
> >>     On Fri, Apr 20, 2018 at 05:59:16PM +0800, Koenig, Christian wrote:
> >>     > Am 20.04.2018 um 11:40 schrieb Huang Rui:
> >>     > > "aaabaf4   drm/amdgpu: defer test IBs on the rings at boot (V3)"
> >>     > > Above patch defers the execution of gfx/compute ib tests. However, at
> >>     that time,
> >>     > > the gfx may already go into idle state. If "idle" gfx receives command
> >>     > > submission, it will get hang in the system. So we must add is_gfx_on
> >>     checking at
> >>     > > start of ib tests.
> >>     >
> >>     > Do I see that right that you just skip the IB test when the GFX block is
> >>     > already turned of? In this case that would be a clear NAK.
> >>     >
> >>     > BTW: How do you detect that we need to turn GFX on again?
> >>
> >>     Christian, I know point. But there is a hang issue if we would like try to
> >>     disable/enable gfxoff with SMC message at runtime. Actually, I am trying to
> >>     find a good sequence to fix it. After that, I can even expose an debugfs
> >>     interface to configure that. So I have to skip the test for the moment when
> >>     gfx is in "idle".
> >>
> >>
> >> Working around that issue for the moment is ok, but please note that explicitly
> >> in both the commit message and a code comment.
> >
> > OK. Will add it at V2.
> >
> >>
> >> But don't you run into the same problem when the UMD starts to submit commands?
> >
> > When UMD starts, RLC firmware will detect the "draw" command, then it will
> > power up gfx. So it won't have problem at that time. The mainly state
> > machine doesn't expose to driver side yet.
> >
> >>
> >> I mean the idea of the IB test is that you "simulate" an userspace command
> >> submission and see if it works.
> >>
> >
> > Yes, agree. Any idea to "simulate" the "draw" command? Or please wait for
> > my fix for enabling/disabling gfxoff at runtime.
> 
> 
> Is there some special formatting in the IB required?  I don't really
> see how this will work.  There is likely tons of state before the
> actual draw command in the IB.
> 

No, there isn't. The mainly behavior to turn on/off gfx is almost in RLC
firmware. From driver's perspective, we only just use smc mesg to
enable/disable the feature.

Thanks,
Ray