[PATCH v6 10/14] drm/print: Add drm_debug_category_printer

[Sean Paul]

From: Sean Paul <seanpaul at chromium.org>

This patch adds a new printer which will select the appropriate output
for a given debug category. Currently there is only one output target,
which is syslog. However in the future we'll have tracefs and it will be
useful to print to syslog, tracefs, or both. Drivers just need to create
the printer for the appropriate category and the printer will decide
where to send the output.

Signed-off-by: Sean Paul <seanpaul at chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200608210505.48519-11-sean@poorly.run #v5

Changes in v5:
-Added to the set
Changes in v6:
-None
---
 drivers/gpu/drm/drm_print.c |  5 +++++
 include/drm/drm_print.h     | 28 ++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index 2ff7a6ecc632..4d984a01b3a3 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -172,6 +172,11 @@ void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf)
 }
 EXPORT_SYMBOL(__drm_printfn_err);
 
+void __drm_printfn_noop(struct drm_printer *p, struct va_format *vaf)
+{
+}
+EXPORT_SYMBOL(__drm_printfn_noop);
+
 /**
  * drm_puts - print a const string to a &drm_printer stream
  * @p: the &drm printer
diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
index ce7675bf0d2b..8987b98bbfda 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -87,6 +87,7 @@ void __drm_puts_seq_file(struct drm_printer *p, const char *str);
 void __drm_printfn_info(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_debug_syslog(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf);
+void __drm_printfn_noop(struct drm_printer *p, struct va_format *vaf);
 
 __printf(2, 3)
 void drm_printf(struct drm_printer *p, const char *f, ...);
@@ -329,6 +330,33 @@ static inline bool drm_debug_enabled(enum drm_debug_category category)
 	return drm_debug_syslog_enabled(category);
 }
 
+/**
+ * drm_debug_category_printer - construct a &drm_printer that outputs to
+ * pr_debug() if enabled for the given category.
+ * @category: the DRM_UT_* message category this message belongs to
+ * @prefix: trace output prefix
+ *
+ * RETURNS:
+ * The &drm_printer object
+ */
+static inline struct drm_printer
+drm_debug_category_printer(enum drm_debug_category category,
+			   const char *prefix)
+{
+	struct drm_printer p = {
+		.prefix = prefix
+	};
+
+	if (drm_debug_syslog_enabled(category)) {
+		p.printfn = __drm_printfn_debug_syslog;
+	} else {
+		WARN(1, "Debug category %d is inactive.", category);
+		p.printfn = __drm_printfn_noop;
+	}
+
+	return p;
+}
+
 /*
  * struct device based logging
  *
-- 
Sean Paul, Software Engineer, Google / Chromium OS