[Intel-gfx] [RFC] drm/i915/guc: Keep GuC log disabled by default

[Chris Wilson]

Quoting Michał Winiarski (2018-01-19 13:36:27)
> On Fri, Jan 19, 2018 at 12:49:26PM +0000, Michal Wajdeczko wrote:
> > It looks that GuC log functionality is not fully functional yet and
> > causes issues when enabled by auto(-1) modparam on debug builds.
> > 
> > [   30.062893] ======================================================
> > [   30.062894] WARNING: possible circular locking dependency detected
> > [   30.062895] 4.15.0-rc8-CI-CI_DRM_3648+ #1 Tainted: G     U
> > [   30.062896] ------------------------------------------------------
> > [   30.062897] debugfs_test/1268 is trying to acquire lock:
> > [   30.062898]  (&dev->struct_mutex){+.+.}, at: [<00000000e4213449>] i915_mutex_lock_interruptible+0x47/0x130 [i915]
> > [   30.062921]
> >                but task is already holding lock:
> > [   30.062921]  (&mm->mmap_sem){++++}, at: [<00000000dd7adc93>] __do_page_fault+0x106/0x560
> > [   30.062924]
> >                which lock already depends on the new lock.
> > 
> 
> I'd leave the lockdep splat out of here, since that's just the tip of the
> iceberg :)
> 
> > Fixes: 0ed87953532652 ("drm/i915/guc: Redefine guc_log_level modparam values")
> 
> s/Fixes/References
> 
> It allows us to get test results while we're fixing the logging issues, so:
> 
> Reviewed-by: Michał Winiarski <michal.winiarski at intel.com>

I agree. It's a mess, but disabling it for now lets CI provide test
coverage and early warning for new breakage. So pushed, even though it's
an RFC.
-Chris