linux-kernel - [PATCH v11 13/19] drm_print: refine drm_debug

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Date:   Thu,  6 Jan 2022 22:29:36 -0700
From:   Jim Cromie <jim.cromie@...il.com>
To:     jbaron@...mai.com, gregkh@...uxfoundation.org,
        linux@...musvillemoes.dk, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, daniel.vetter@...ll.ch,
        seanpaul@...omium.org, robdclark@...il.com,
        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:     quic_saipraka@...cinc.com, will@...nel.org,
        catalin.marinas@....com, quic_psodagud@...cinc.com, maz@...nel.org,
        arnd@...db.de, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, mingo@...hat.com,
        jim.cromie@...il.com
Subject: [PATCH v11 13/19] drm_print: refine drm_debug_enabled for dyndbg+jump-label

In order to use dynamic-debug's jump-label optimization in drm-debug,
its clarifying to refine drm_debug_enabled into 3 uses:

1.   drm_debug_enabled - legacy, public
2. __drm_debug_enabled - optimized for dyndbg jump-label enablement.
3.  _drm_debug_enabled - pr_debug instrumented, observable

1. The legacy version always checks the bits.

2. is privileged, for use by __drm_dbg(), __drm_dev_dbg(), which do an
early return unless the category is enabled (free of call/NOOP side
effects).  For dyndbg builds, debug callsites are selectively
"pre-enabled", so __drm_debug_enabled() short-circuits to true there.
Remaining callers of 1 may be able to use 2, case by case.

3. is 1st wrapped in a macro, with a pr_debug, which reports each
usage in /proc/dynamic_debug/control, making it observable in the
logs.  The macro lets the pr_debug see the real caller, not the inline
function.

When plugged into 1, it identified ~10 remaining callers of the
function, leading to the follow-on cleanup patch, and would allow
activating the pr_debugs, estimating the callrate, and the potential
savings by using the wrapper macro.

It is unused ATM, but it fills out the picture.

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 drivers/gpu/drm/drm_print.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index 5dd6713c14f2..aab29dd6cad1 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -265,7 +265,7 @@ void __drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
 	struct va_format vaf;
 	va_list args;

-	if (!drm_debug_enabled(category))
+	if (!__drm_debug_enabled(category))
 		return;

 	va_start(args, format);
@@ -290,7 +290,7 @@ void ___drm_dbg(enum drm_debug_category category, const char *format, ...)
 	struct va_format vaf;
 	va_list args;

-	if (!drm_debug_enabled(category))
+	if (!__drm_debug_enabled(category))
 		return;

 	va_start(args, format);
-- 
2.33.1