linux-kernel - Re: [Intel-gfx] [PATCH 1/7] drm: mark drm.debug-on-dyndbg as BROKEN for now

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Message-ID: <Y3IynYl3Ejb6NTAd@intel.com>
Date:   Mon, 14 Nov 2022 14:20:45 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Jim Cromie <jim.cromie@...il.com>
Cc:     jbaron@...mai.com, gregkh@...uxfoundation.org,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        daniel.vetter@...ll.ch, linux@...musvillemoes.dk,
        seanpaul@...omium.org, joe@...ches.com
Subject: Re: [Intel-gfx] [PATCH 1/7] drm: mark drm.debug-on-dyndbg as BROKEN
 for now

On Fri, Nov 11, 2022 at 03:17:09PM -0700, Jim Cromie wrote:
> drm.debug-on-dyndbg has a regression, due to a chicken-egg
> initialization problem:
> 
> 1- modprobe i915
>    i915 needs drm.ko, which is loaded 1st
> 
> 2- "modprobe drm drm.debug=0x1ff" (virtual/implied)
>    drm.debug is set post-initialization, from boot-args etc
> 
> 3- `modprobe i915` finishes
> 
> W/O drm.debug-on-dyndbg that just works, because all drm_dbg*
> callsites use drm_debug_enabled() to check __drm_debug & DEM_UT_<CAT>
> before printing.
> 
> But the whole point of drm.debug-on-dyndbg is to avoid that runtime
> test, by enabling (at post-modinit) a static-key at each callsite in
> the just-loaded module.
> 
> And since drm.ko is loaded before all dependent modules, none are
> "just-loaded", and no drm.debug callsites are present yet, except
> those in drm.ko itself.
> 
> Signed-off-by: Jim Cromie <jim.cromie@...il.com>
> ---
>  drivers/gpu/drm/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 34f5a092c99e..0d1e59e6bb7e 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -54,6 +54,7 @@ config DRM_DEBUG_MM
>  config DRM_USE_DYNAMIC_DEBUG
>  	bool "use dynamic debug to implement drm.debug"
>  	default y

Could you switch to 'default n' as well? i915 CI actually enables
BROKEN so that we can test some more experimental stuff which is
hidden behind BROKEN for normal users.

> +	depends on BROKEN	# chicken-egg initial enable problem
>  	depends on DRM
>  	depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE
>  	depends on JUMP_LABEL
> -- 
> 2.38.1

-- 
Ville Syrjälä
Intel