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Date:   Thu, 17 Nov 2022 07:29:00 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Jim Cromie <jim.cromie@gmail.com>
Cc:     jbaron@akamai.com, dri-devel@lists.freedesktop.org,
        amd-gfx@lists.freedesktop.org, intel-gvt-dev@lists.freedesktop.org,
        intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        daniel.vetter@ffwll.ch, seanpaul@chromium.org, robdclark@gmail.com,
        linux@rasmusvillemoes.dk, joe@perches.com
Subject: Re: [PATCH 1/7] drm: mark drm.debug-on-dyndbg as BROKEN for now
Message-ID: <Y3XUrOGAV4I7bB3M@kroah.com>
References: <20220912052852.1123868-1-jim.cromie@gmail.com>
 <20221111221715.563020-1-jim.cromie@gmail.com>
 <20221111221715.563020-2-jim.cromie@gmail.com>
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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@gmail.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
> +	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

This should go through the drm tree now.  The rest probably should also
go that way and not through my tree as well.

thanks,

greg k-h