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

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

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>

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
>