linux-kernel - [PATCH v11 14/19] drm_print: prefer bare printk KERN

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Date:   Thu,  6 Jan 2022 22:29:37 -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 14/19] drm_print: prefer bare printk KERN_DEBUG on generic fn

drm_print.c calls pr_debug() just once, from __drm_printfn_debug(),
which is a generic/service fn.  The callsite is compile-time enabled
by DEBUG in both DYNAMIC_DEBUG=y/n builds.

For dyndbg builds, reverting this callsite back to bare printk is
correcting a few anti-features:

1- callsite is generic, serves multiple drm users.
   its hardwired on currently
   could accidentally: #> echo -p > /proc/dynamic_debug/control

2- optional "decorations" by dyndbg are unhelpful/misleading
   they describe only the generic site, not end users

IOW, 1,2 are unhelpful at best, and possibly confusing.

reverting yields a nominal data and text shrink:

   text    data     bss     dec     hex filename
 462583   36604   54592 553779   87333 /lib/modules/5.16.0-rc4-lm1-00008-ged3eac8ceeea/kernel/drivers/gpu/drm/drm.ko
 462515   36532   54592 553639   872a7 /lib/modules/5.16.0-rc4-lm1-00009-g6ce0b88d2539-dirty/kernel/drivers/gpu/drm/drm.ko

NB: this was noticed using _drm_debug_enabled(), added earlier.

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 drivers/gpu/drm/drm_print.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index aab29dd6cad1..b911f949af5b 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -23,8 +23,6 @@
  * Rob Clark <robdclark@...il.com>
  */
 
-#define DEBUG /* for pr_debug() */
-
 #include <linux/stdarg.h>
 
 #include <linux/io.h>
@@ -165,7 +163,8 @@ EXPORT_SYMBOL(__drm_printfn_info);
 
 void __drm_printfn_debug(struct drm_printer *p, struct va_format *vaf)
 {
-	pr_debug("%s %pV", p->prefix, vaf);
+	/* pr_debug callsite decorations are unhelpful here */
+	printk(KERN_DEBUG "%s %pV", p->prefix, vaf);
 }
 EXPORT_SYMBOL(__drm_printfn_debug);
 
-- 
2.33.1