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From:   Jim Cromie <jim.cromie@gmail.com>
To:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Cc:     jbaron@akamai.com, Jim Cromie <jim.cromie@gmail.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>
Subject: [RFC PATCH 1/2] drm: RFC add choice to use dynamic debug in drm-debug
Date:   Thu,  3 Dec 2020 20:53:17 -0700
Message-Id: <20201204035318.332419-2-jim.cromie@gmail.com>
In-Reply-To: <20201204035318.332419-1-jim.cromie@gmail.com>
References: <20201204035318.332419-1-jim.cromie@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

drm's debug system uses distinct categories of debug messages, mapped
to bits in drm.debug.  Currently, code does a lot of unlikely bit-mask
checks on drm.debug (in drm_debug_enabled), we can use dynamic debug
instead, and get all that jump_label goodness.

RFC: dynamic debug has no concept of category, but we can do without
one if we can prepend a class-prefix to each printk format.  Then we
can use "format ^prefix" to select the whole category with one query.
This is a log-facing and user visible change, but it seems unlikely to
cause trouble for log watchers; they're not relying on the absence of
class prefix strings.

This conversion yields ~2100 new callsites on my i7 laptop:

  dyndbg: 195 debug prints in module drm_kms_helper
  dyndbg: 298 debug prints in module drm
  dyndbg: 1630 debug prints in module i915

Since this change has wide-ranging effects (many drm drivers, with
many callsites, and kernel image growth), and most vendors don't
enable DYNAMIC_DEBUG, we supplement the existing mechanism, adding
CONFIG_DRM_USE_DYNAMIC_DEBUG to enable the new one.

The indirection/switchover has a few parts:

1 a new callback on drm.debug which calls dynamic_debug_exec_queries
  to map those bits to specific query/commands
  dynamic_debug_exec_queries("format ^drm:kms: +p", "drm*");

2 a "converted" or "classy" DRM_UT_* map
  similar to DRM_UT_* ( symbol => bit-mask )
  named it  cDRM_UT_* ( symbol => format-class-prefix-string )

  cDRM_UT_* is either ( CONFIG_DRM_USE_DYNAMIC_DEBUG )
  legacy: cDRM_UT_* <-- DRM_UT_*
  enabled:
  +#define cDRM_UT_KMS    "drm:kms: "
  +#define cDRM_UT_PRIME  "drm:prime: "
  +#define cDRM_UT_ATOMIC "drm:atomic: "

  these are similar to "gvt: cmd:" in i915/gvt
  and effectively a replacement for DRM_NAME
  please bikeshed on keys, values. latter are log-facing.

3 drm_dev_dbg & drm_debug are renamed (prefixed with '_')
  old names are now macros, which are ifdefd
  legacy:  -> to renamed fn
  enabled: -> dev_dbg & pr_debug, after prepending prefix to format.

4 names in (2) are called from DRM_DEBUG_<Category> and drm_dbg_<Category>.
  all these get "converted" to use cDRM_UT_*, to get right token type.

RFC: for dynamic debug, category is a source-facing addition;
something like pr_debug_cat(cat, ...) would do it, iff cat is a
compile-time const.  Note that cat isn't needed in the printing, it
would be saved into a new field in struct _ddebug, and used only for
callsite selection, activation and control.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 drivers/gpu/drm/Kconfig     | 13 ++++++
 drivers/gpu/drm/drm_print.c | 75 ++++++++++++++++++++++++++++--
 include/drm/drm_print.h     | 92 +++++++++++++++++++++++++++----------
 3 files changed, 153 insertions(+), 27 deletions(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 147d61b9674e..854bc1ad21fb 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -54,6 +54,19 @@ config DRM_DEBUG_MM
 
 	  If in doubt, say "N".
 
+config DRM_USE_DYNAMIC_DEBUG
+	bool "use dynamic debug to implement drm.debug"
+	default n
+	depends on DRM
+	depends on DYNAMIC_DEBUG
+	depends on JUMP_LABEL
+	help
+	  The drm debug category facility does a lot of unlikely bit-field
+	  tests at runtime; while cheap individually, the cost accumulates.
+	  This option uses dynamic debug facility (if configured and
+	  using jump_label) to avoid those runtime checks, patching
+	  the kernel when those debugs are desired.
+
 config DRM_DEBUG_SELFTEST
 	tristate "kselftests for DRM"
 	depends on DRM
diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index 111b932cf2a9..e2acdfc7088b 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -52,8 +52,75 @@ MODULE_PARM_DESC(debug, "Enable debug output, where each bit enables a debug cat
 "\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n"
 "\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n"
 "\t\tBit 8 (0x100) will enable DP messages (displayport code)");
+
+#ifndef CONFIG_DRM_USE_DYNAMIC_DEBUG
 module_param_named(debug, __drm_debug, int, 0600);
 
+#else
+static char *format_class_prefixes[] = {
+	cDRM_UT_CORE,
+	cDRM_UT_DRIVER,
+	cDRM_UT_KMS,
+	cDRM_UT_PRIME,
+	cDRM_UT_ATOMIC,
+	cDRM_UT_VBL,
+	cDRM_UT_STATE,
+	cDRM_UT_LEASE,
+	cDRM_UT_DP,
+	cDRM_UT_DRMRES
+};
+
+#define OUR_QUERY_SIZE 64 /* > strlen "format '^%s' %cp" + longest prefix */
+
+static int param_set_dyndbg(const char *instr, const struct kernel_param *kp)
+{
+	unsigned int val;
+	unsigned long changes, result;
+	int rc, chgct = 0, totct = 0, bitpos;
+	char query[OUR_QUERY_SIZE];
+
+	rc = kstrtouint(instr, 0, &val);
+	if (rc) {
+		pr_err("%s: failed\n", __func__);
+		return -EINVAL;
+	}
+	result = val;
+	changes = result ^ __drm_debug;
+
+	pr_debug("changes:0x%lx from result:0x%lx\n", changes, result);
+
+	for_each_set_bit(bitpos, &changes, ARRAY_SIZE(format_class_prefixes)) {
+
+		sprintf(query, "format '^%s' %cp", format_class_prefixes[bitpos],
+			test_bit(bitpos, &result) ? '+' : '-');
+
+		chgct = dynamic_debug_exec_queries(query, "drm*");
+		if (chgct < 0) {
+			pr_err("%s: exec err:%d on: %s\n", __func__, chgct, query);
+			continue;
+		}
+		pr_debug("change ct:%d on %s\n", chgct, query);
+		totct += chgct;
+	}
+	pr_debug("total changes: %d\n", totct);
+	__drm_debug = result;
+	return 0;
+}
+
+static int param_get_dyndbg(char *buffer, const struct kernel_param *kp)
+{
+	pr_debug("debug-val:0x%x %u\n", __drm_debug, *((unsigned int *)kp->arg));
+	return scnprintf(buffer, PAGE_SIZE, "%u\n",
+			 *((unsigned int *)kp->arg));
+}
+static const struct kernel_param_ops param_ops_debug = {
+	.set = param_set_dyndbg,
+	.get = param_get_dyndbg,
+};
+module_param_cb(debug, &param_ops_debug, &__drm_debug, 0644);
+
+#endif /* CONFIG_DRM_USE_DYNAMIC_DEBUG */
+
 void __drm_puts_coredump(struct drm_printer *p, const char *str)
 {
 	struct drm_print_iterator *iterator = p->arg;
@@ -256,7 +323,7 @@ void drm_dev_printk(const struct device *dev, const char *level,
 }
 EXPORT_SYMBOL(drm_dev_printk);
 
-void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
+void _drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
 		 const char *format, ...)
 {
 	struct va_format vaf;
@@ -278,9 +345,9 @@ void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
 
 	va_end(args);
 }
-EXPORT_SYMBOL(drm_dev_dbg);
+EXPORT_SYMBOL(_drm_dev_dbg);
 
-void __drm_dbg(enum drm_debug_category category, const char *format, ...)
+void ___drm_dbg(enum drm_debug_category category, const char *format, ...)
 {
 	struct va_format vaf;
 	va_list args;
@@ -297,7 +364,7 @@ void __drm_dbg(enum drm_debug_category category, const char *format, ...)
 
 	va_end(args);
 }
-EXPORT_SYMBOL(__drm_dbg);
+EXPORT_SYMBOL(___drm_dbg);
 
 void __drm_err(const char *format, ...)
 {
diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
index f32d179e139d..2bd5c38aa100 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -319,6 +319,51 @@ enum drm_debug_category {
 	DRM_UT_DRMRES		= 0x200,
 };
 
+#if !defined(CONFIG_DRM_USE_DYNAMIC_DEBUG)
+
+/* Use legacy drm-debug functions, implying drm_debug_enabled().
+ * For cDRM_UT_* (converted category), identity map to DRM_UT_*
+ */
+#define __drm_dbg(cls, fmt, ...)					\
+	___drm_dbg(cls, fmt, ##__VA_ARGS__)
+#define drm_dev_dbg(dev, cls, fmt, ...)					\
+	_drm_dev_dbg(dev, cls, fmt, ##__VA_ARGS__)
+
+#define cDRM_UT_CORE	DRM_UT_CORE
+#define cDRM_UT_DRIVER	DRM_UT_DRIVER
+#define cDRM_UT_KMS	DRM_UT_KMS
+#define cDRM_UT_PRIME	DRM_UT_PRIME
+#define cDRM_UT_ATOMIC	DRM_UT_ATOMIC
+#define cDRM_UT_VBL	DRM_UT_VBL
+#define cDRM_UT_STATE	DRM_UT_STATE
+#define cDRM_UT_LEASE	DRM_UT_LEASE
+#define cDRM_UT_DP	DRM_UT_DP
+#define cDRM_UT_DRMRES	DRM_UT_DRMRES
+
+#else /* CONFIG_DRM_USE_DYNAMIC_DEBUG */
+
+/* use dynamic_debug to avoid drm_debug_enabled.
+ * dyndbg has no category, so we prefix format with a class-string,
+ * and alter cDRM_UT_* to provide those class strings
+ */
+#define __drm_dbg(cls, fmt, ...)					\
+	pr_debug(cls # fmt, ##__VA_ARGS__)
+#define drm_dev_dbg(dev, cls, fmt, ...)					\
+	dev_dbg(dev, cls fmt, ##__VA_ARGS__)
+
+#define cDRM_UT_CORE	"drm:core: "
+#define cDRM_UT_DRIVER	"drm:drvr: "
+#define cDRM_UT_KMS	"drm:kms: "
+#define cDRM_UT_PRIME	"drm:prime: "
+#define cDRM_UT_ATOMIC	"drm:atomic: "
+#define cDRM_UT_VBL	"drm:vbl: "
+#define cDRM_UT_STATE	"drm:state: "
+#define cDRM_UT_LEASE	"drm:lease: "
+#define cDRM_UT_DP	"drm:dp: "
+#define cDRM_UT_DRMRES	"drm:res "
+
+#endif /* !CONFIG_DRM_USE_DYNAMIC_DEBUG */
+
 static inline bool drm_debug_enabled(enum drm_debug_category category)
 {
 	return unlikely(__drm_debug & category);
@@ -334,7 +379,7 @@ __printf(3, 4)
 void drm_dev_printk(const struct device *dev, const char *level,
 		    const char *format, ...);
 __printf(3, 4)
-void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
+void _drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
 		 const char *format, ...);
 
 /**
@@ -383,7 +428,7 @@ void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
  * @fmt: printf() like format string.
  */
 #define DRM_DEV_DEBUG(dev, fmt, ...)					\
-	drm_dev_dbg(dev, DRM_UT_CORE, fmt, ##__VA_ARGS__)
+	drm_dev_dbg(dev, cDRM_UT_CORE, fmt, ##__VA_ARGS__)
 /**
  * DRM_DEV_DEBUG_DRIVER() - Debug output for vendor specific part of the driver
  *
@@ -391,7 +436,7 @@ void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
  * @fmt: printf() like format string.
  */
 #define DRM_DEV_DEBUG_DRIVER(dev, fmt, ...)				\
-	drm_dev_dbg(dev, DRM_UT_DRIVER,	fmt, ##__VA_ARGS__)
+	drm_dev_dbg(dev, cDRM_UT_DRIVER, fmt, ##__VA_ARGS__)
 /**
  * DRM_DEV_DEBUG_KMS() - Debug output for modesetting code
  *
@@ -443,25 +488,25 @@ void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
 
 
 #define drm_dbg_core(drm, fmt, ...)					\
-	drm_dev_dbg((drm)->dev, DRM_UT_CORE, fmt, ##__VA_ARGS__)
+	drm_dev_dbg((drm)->dev, cDRM_UT_CORE, fmt, ##__VA_ARGS__)
 #define drm_dbg(drm, fmt, ...)						\
-	drm_dev_dbg((drm)->dev, DRM_UT_DRIVER, fmt, ##__VA_ARGS__)
+	drm_dev_dbg((drm)->dev, cDRM_UT_DRIVER, fmt, ##__VA_ARGS__)
 #define drm_dbg_kms(drm, fmt, ...)					\
-	drm_dev_dbg((drm)->dev, DRM_UT_KMS, fmt, ##__VA_ARGS__)
+	drm_dev_dbg((drm)->dev, cDRM_UT_KMS, fmt, ##__VA_ARGS__)
 #define drm_dbg_prime(drm, fmt, ...)					\
-	drm_dev_dbg((drm)->dev, DRM_UT_PRIME, fmt, ##__VA_ARGS__)
+	drm_dev_dbg((drm)->dev, cDRM_UT_PRIME, fmt, ##__VA_ARGS__)
 #define drm_dbg_atomic(drm, fmt, ...)					\
-	drm_dev_dbg((drm)->dev, DRM_UT_ATOMIC, fmt, ##__VA_ARGS__)
+	drm_dev_dbg((drm)->dev, cDRM_UT_ATOMIC, fmt, ##__VA_ARGS__)
 #define drm_dbg_vbl(drm, fmt, ...)					\
-	drm_dev_dbg((drm)->dev, DRM_UT_VBL, fmt, ##__VA_ARGS__)
+	drm_dev_dbg((drm)->dev, cDRM_UT_VBL, fmt, ##__VA_ARGS__)
 #define drm_dbg_state(drm, fmt, ...)					\
-	drm_dev_dbg((drm)->dev, DRM_UT_STATE, fmt, ##__VA_ARGS__)
+	drm_dev_dbg((drm)->dev, cDRM_UT_STATE, fmt, ##__VA_ARGS__)
 #define drm_dbg_lease(drm, fmt, ...)					\
-	drm_dev_dbg((drm)->dev, DRM_UT_LEASE, fmt, ##__VA_ARGS__)
+	drm_dev_dbg((drm)->dev, cDRM_UT_LEASE, fmt, ##__VA_ARGS__)
 #define drm_dbg_dp(drm, fmt, ...)					\
-	drm_dev_dbg((drm)->dev, DRM_UT_DP, fmt, ##__VA_ARGS__)
+	drm_dev_dbg((drm)->dev, cDRM_UT_DP, fmt, ##__VA_ARGS__)
 #define drm_dbg_drmres(drm, fmt, ...)					\
-	drm_dev_dbg((drm)->dev, DRM_UT_DRMRES, fmt, ##__VA_ARGS__)
+	drm_dev_dbg((drm)->dev, cDRM_UT_DRMRES, fmt, ##__VA_ARGS__)
 
 
 /*
@@ -471,7 +516,7 @@ void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
  */
 
 __printf(2, 3)
-void __drm_dbg(enum drm_debug_category category, const char *format, ...);
+void ___drm_dbg(enum drm_debug_category category, const char *format, ...);
 __printf(1, 2)
 void __drm_err(const char *format, ...);
 
@@ -500,29 +545,30 @@ void __drm_err(const char *format, ...);
 #define DRM_ERROR_RATELIMITED(fmt, ...)					\
 	DRM_DEV_ERROR_RATELIMITED(NULL, fmt, ##__VA_ARGS__)
 
+
 #define DRM_DEBUG(fmt, ...)						\
-	__drm_dbg(DRM_UT_CORE, fmt, ##__VA_ARGS__)
+	__drm_dbg(cDRM_UT_CORE, fmt, ##__VA_ARGS__)
 
 #define DRM_DEBUG_DRIVER(fmt, ...)					\
-	__drm_dbg(DRM_UT_DRIVER, fmt, ##__VA_ARGS__)
+	__drm_dbg(cDRM_UT_DRIVER, fmt, ##__VA_ARGS__)
 
 #define DRM_DEBUG_KMS(fmt, ...)						\
-	__drm_dbg(DRM_UT_KMS, fmt, ##__VA_ARGS__)
+	__drm_dbg(cDRM_UT_KMS, fmt, ##__VA_ARGS__)
 
 #define DRM_DEBUG_PRIME(fmt, ...)					\
-	__drm_dbg(DRM_UT_PRIME, fmt, ##__VA_ARGS__)
+	__drm_dbg(cDRM_UT_PRIME, fmt, ##__VA_ARGS__)
 
 #define DRM_DEBUG_ATOMIC(fmt, ...)					\
-	__drm_dbg(DRM_UT_ATOMIC, fmt, ##__VA_ARGS__)
+	__drm_dbg(cDRM_UT_ATOMIC, fmt, ##__VA_ARGS__)
 
 #define DRM_DEBUG_VBL(fmt, ...)						\
-	__drm_dbg(DRM_UT_VBL, fmt, ##__VA_ARGS__)
+	__drm_dbg(cDRM_UT_VBL, fmt, ##__VA_ARGS__)
 
 #define DRM_DEBUG_LEASE(fmt, ...)					\
-	__drm_dbg(DRM_UT_LEASE, fmt, ##__VA_ARGS__)
+	__drm_dbg(cDRM_UT_LEASE, fmt, ##__VA_ARGS__)
 
 #define DRM_DEBUG_DP(fmt, ...)						\
-	__drm_dbg(DRM_UT_DP, fmt, ## __VA_ARGS__)
+	__drm_dbg(cDRM_UT_DP, fmt, ## __VA_ARGS__)
 
 
 #define DRM_DEBUG_KMS_RATELIMITED(fmt, ...)				\
@@ -531,7 +577,7 @@ void __drm_err(const char *format, ...);
 				      DEFAULT_RATELIMIT_INTERVAL,       \
 				      DEFAULT_RATELIMIT_BURST);         \
 	if (__ratelimit(&_rs))						\
-		drm_dev_dbg(NULL, DRM_UT_KMS, fmt, ##__VA_ARGS__);	\
+		drm_dev_dbg(NULL, cDRM_UT_KMS, fmt, ##__VA_ARGS__);	\
 })
 
 /*
-- 
2.28.0