[Intel-gfx] Warning: Broadwell/i915: Unclaimed register detected before reading register 0x130040

[Daniel Vetter]

On Mon, Jun 15, 2015 at 11:47:46AM +0100, Chris Wilson wrote:
> On Mon, Jun 15, 2015 at 12:25:10PM +0200, Daniel Vetter wrote:
> > On Mon, May 25, 2015 at 08:04:45PM +0200, Dominik Brodowski wrote:
> > > Hey,
> > > 
> > > this just popped up in the dmesg of my Dell XPS 13 -- the system seems to
> > > run well, but still, it asks about being cut and sent, so here it is. It is
> > > on 4.1.0-rc4+ (Linus' tree as of May 24th, around 3pm UTC -- don't have the
> > > git commit ID anymore).
> > 
> > Can you please boot with i915.mmio_debug=10 and try to reproduce the
> > issue? 
> 
> It won't help. To see this WARN implies that hsw_unclaimed_reg_detect()
> fired and mmio debugging is enabled, and the WARN then fires before a
> subsequent register access. So it implies the unclaimed register is not
> being accessed by the display driver -- presuming that we have wrapped
> all register access appropriately.
> 
> <invalid register access>
> hsw_unclaimed_reg_detect -> fires, clears the invalid flag
> ...
> (
> 	hsw_unclaimed_reg_debug before
> 	mmio
> 	hsw_unclaimed_reg_debug  after
> ) -> nothing x N
> ...
> <invalid register access>
> hsw_unclaimed_reg_debug -> fires before, ergo no more useful information
> 
> Or else I nerfed the automatic debugging too much.

Hm I thought it's also gating some of the interrupt frobbery, but that
doesn't exist on bdw anyway. It would be still good to figure out who's
stomping all over the gpu though.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch