Re: [PATCH] drm/i915: Improve debug Kconfig texts a bit

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Jul 05, 2021 at 02:48:23PM +0300, Joonas Lahtinen wrote:
> Quoting Daniel Vetter (2021-07-02 23:17:08)
> > We're not consistently recommending these for developers only.
> > 
> > I stumbled over this due to DRM_I915_LOW_LEVEL_TRACEPOINTS, which was
> > added in
> > 
> > commit 354d036fcf70654cff2e2cbdda54a835d219b9d2
> > Author: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > Date:   Tue Feb 21 11:01:42 2017 +0000
> > 
> >     drm/i915/tracepoints: Add request submit and execute tracepoints
> > 
> > to "alleviate the performance impact concerns."
> > 
> > Which is nonsense.
> 
> I think that was the original reason why the patch was developed and
> it got merged primarily for the latter reason. Unfortunately the patch
> commit messages don't always get rewritten.
> 
> > Tvrtko and Joonas pointed out on irc that the real (but undocumented
> > reason) was stable abi concerns for tracepoints, see
> > 
> > https://lwn.net/Articles/705270/
> > 
> > and the specific change that was blocked around tracepoints:
> > 
> > https://lwn.net/Articles/442113/
> > 
> > Anyway to make it a notch clearer why we have this Kconfig option
> > consistly add the "Recommended for driver developers only." to it and
> > all the other debug options we have.
> > 
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > Cc: Matthew Brost <matthew.brost@intel.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> 
> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Pushed to drm-intel-gt-next, thanks for taking a look.
-Daniel

> 
> Regards, Joonas
> 
> > ---
> >  drivers/gpu/drm/i915/Kconfig.debug | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
> > index 2ca88072d30f..f27c0b5873f7 100644
> > --- a/drivers/gpu/drm/i915/Kconfig.debug
> > +++ b/drivers/gpu/drm/i915/Kconfig.debug
> > @@ -215,6 +215,8 @@ config DRM_I915_LOW_LEVEL_TRACEPOINTS
> >           This provides the ability to precisely monitor engine utilisation
> >           and also analyze the request dependency resolving timeline.
> >  
> > +         Recommended for driver developers only.
> > +
> >           If in doubt, say "N".
> >  
> >  config DRM_I915_DEBUG_VBLANK_EVADE
> > @@ -228,6 +230,8 @@ config DRM_I915_DEBUG_VBLANK_EVADE
> >           is exceeded, even if there isn't an actual risk of missing
> >           the vblank.
> >  
> > +         Recommended for driver developers only.
> > +
> >           If in doubt, say "N".
> >  
> >  config DRM_I915_DEBUG_RUNTIME_PM
> > @@ -240,4 +244,6 @@ config DRM_I915_DEBUG_RUNTIME_PM
> >           runtime PM functionality. This may introduce overhead during
> >           driver loading, suspend and resume operations.
> >  
> > +         Recommended for driver developers only.
> > +
> >           If in doubt, say "N"
> > -- 
> > 2.32.0.rc2
> > 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch