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

[Chris Wilson]

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.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre