[Intel-gfx] [PATCH 1/2] drm/i915: Track last register written (debug)

[Chris Wilson]

On Fri, Feb 20, 2015 at 09:55:09AM -0200, Paulo Zanoni wrote:
> 2015-02-20 3:33 GMT-02:00 Ben Widawsky <benjamin.widawsky at intel.com>:
> > Register writes are supposed to be posted, and therefore "fast." In order to try
> > to preserve this behavior, the patch uses percpu variables to make the overhead
> > minimal. The slow data collection is done at error time, and that only occurs if
> > the user specified mmio_debug=1 module parameter.
> >
> > I wrote this patch to try to track down annoying and sporadic errors on my
> > Broadwell laptop. Sometimes it's obvious how you got to this point from the
> > backtrace, but other times it isn't.
> >
> 
> Register reads can also trigger the unclaimed register error. Don't
> you want to also record the last one we read on each CPU too?
> 
> Also, just to remind you since you seem to be debugging something:
> user space programs (such as intel_reg_dumper or anything else) and
> other Kernel modules (like vgacon and others) can also trigger these
> errors, and we can't easily catch these cases.
> 
> Pinging Chris since he always has some ideas about this code.

In this case it is probably better to look at the automatic oneshot
mmio_debug patch.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre