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

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Date:   Fri, 11 Nov 2022 15:17:09 -0700
From:   Jim Cromie <jim.cromie@...il.com>
To:     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
Cc:     daniel.vetter@...ll.ch, seanpaul@...omium.org, robdclark@...il.com,
        linux@...musvillemoes.dk, joe@...ches.com,
        Jim Cromie <jim.cromie@...il.com>
Subject: [PATCH 1/7] drm: mark drm.debug-on-dyndbg as BROKEN for now

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
+	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