[Intel-gfx] [PATCH v3] drm/i915: Disable the mmio.debug WARN after it fires

[Chris Wilson]

On Thu, Dec 18, 2014 at 02:36:54PM +0200, Jani Nikula wrote:
> On Thu, 18 Dec 2014, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > If we have a single unclaimed register, we will have lots. A WARN for
> > each one makes the machine unusable and does not aid debugging. Convert
> > the i915.mmio_debug option to a counter for how many WARNs to fire
> > before shutting up. Even when i915.mmio_debug was disabled it would
> > continue to shout an *ERROR* for every interrupt, without any
> > information at all for debugging.
> >
> > The massive verbiage was added in
> > commit 5978118c39c2f72fd8b39ef9c086723542384809
> > Author: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > Date:   Wed Jul 16 17:49:29 2014 -0300
> >
> >     drm/i915: reorganize the unclaimed register detection code
> >
> > v2: Automatically enable invalid mmio reporting for the *next* invalid
> > access if mmio_debug is disabled by default. This should give us clearer
> > debug information without polluting the logs too much.
> > v3: Compile fixes, rebase.
> >
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Rodrigo Vivi <rodrigo.vivi at gmail.com>
> > Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> > ---
> >  drivers/gpu/drm/i915/i915_drv.h     |  2 +-
> >  drivers/gpu/drm/i915/i915_params.c  |  6 +++---
> >  drivers/gpu/drm/i915/intel_uncore.c | 10 ++++++++--
> >  3 files changed, 12 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > index 3047291ff2b9..ca9e21545063 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -2430,7 +2430,7 @@ struct i915_params {
> >  	bool disable_display;
> >  	bool disable_vtd_wa;
> >  	int use_mmio_flip;
> > -	bool mmio_debug;
> > +	int mmio_debug;
> >  	bool verbose_state_checks;
> >  };
> >  extern struct i915_params i915 __read_mostly;
> > diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> > index 07252d8dc726..43c1df830531 100644
> > --- a/drivers/gpu/drm/i915/i915_params.c
> > +++ b/drivers/gpu/drm/i915/i915_params.c
> > @@ -170,10 +170,10 @@ module_param_named(use_mmio_flip, i915.use_mmio_flip, int, 0600);
> >  MODULE_PARM_DESC(use_mmio_flip,
> >  		 "use MMIO flips (-1=never, 0=driver discretion [default], 1=always)");
> >  
> > -module_param_named(mmio_debug, i915.mmio_debug, bool, 0600);
> > +module_param_named(mmio_debug, i915.mmio_debug, int, 0600);
> >  MODULE_PARM_DESC(mmio_debug,
> > -	"Enable the MMIO debug code (default: false). This may negatively "
> > -	"affect performance.");
> > +	"Enable the MMIO debug code (default: off). "
> > +	"This may negatively affect performance.");
> 
> Why not describe the new behaviour here instead of a comment in
> intel_uncore.c?

Secrets and wording.
"Enable the MMIO debug code for the first N failures (default: off). "

> >  module_param_named(verbose_state_checks, i915.verbose_state_checks, bool, 0600);
> >  MODULE_PARM_DESC(verbose_state_checks,
> > diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> > index e9561de382aa..a3b662de1bdb 100644
> > --- a/drivers/gpu/drm/i915/intel_uncore.c
> > +++ b/drivers/gpu/drm/i915/intel_uncore.c
> > @@ -722,18 +722,24 @@ hsw_unclaimed_reg_debug(struct drm_i915_private *dev_priv, u32 reg, bool read,
> >  		WARN(1, "Unclaimed register detected %s %s register 0x%x\n",
> >  		     when, op, reg);
> >  		__raw_i915_write32(dev_priv, FPGA_DBG, FPGA_DBG_RM_NOCLAIM);
> > +		i915.mmio_debug--; /* Only report the first N failures */
> >  	}
> >  }
> >  
> >  static void
> >  hsw_unclaimed_reg_detect(struct drm_i915_private *dev_priv)
> >  {
> > -	if (i915.mmio_debug)
> > +	static bool mmio_debug_once = true;
> > +
> > +	if (i915.mmio_debug || !mmio_debug_once)
> >  		return;
> >  
> >  	if (__raw_i915_read32(dev_priv, FPGA_DBG) & FPGA_DBG_RM_NOCLAIM) {
> > -		DRM_ERROR("Unclaimed register detected. Please use the i915.mmio_debug=1 to debug this problem.");
> > +		DRM_DEBUG("Unclaimed register detected, "
> > +			  "enabling oneshot unclaimed register reporting. "
> > +			  "Please use i915.mmio_debug=N for more information.\n");
> >  		__raw_i915_write32(dev_priv, FPGA_DBG, FPGA_DBG_RM_NOCLAIM);
> > +		i915.mmio_debug = mmio_debug_once--;
> 
> /me frowns upon the bool assignment to int and bool post-decrement. It's
> not quite IOCCC but a demonstration of things that suck about C.
> 
> Is it on purpose that, if you've set i915.mmio_debug=N, you first
> decrement it to zero, then enter here and set i915.mmio_debug=1 to do
> hsw_unclaimed_reg_debug once more?

Only in that, it serves as a nice post-script "oi, there are more
errors" and that tracking been here, done that was growing the scope
of the patch. N+2 messages is a small price to pay for having a single
more accurate mmio warning in the dmesg rather than an unending torrent
of "*ERROR* there is a problem, but we can't tell you what".
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre