[PATCH v2] drm/print: Introduce drm_line_printer

[Michal Wajdeczko <michal.wajdeczko@xxxxxxxxx>]

This drm printer wrapper can be used to increase the robustness of
the captured output generated by any other drm_printer to make sure
we didn't lost any intermediate lines of the output by adding line
numbers to each output line. Helpful for capturing some crash data.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@xxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
Cc: John Harrison <John.C.Harrison@xxxxxxxxx>
---
v2: don't abuse prefix, use union instead (Jani)
    don't use 'dp' as name, prefer 'p' (Jani)
    add support for unique series identifier (John)
---
 drivers/gpu/drm/drm_print.c | 14 ++++++++
 include/drm/drm_print.h     | 68 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 81 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index cf2efb44722c..be9cbebff5b3 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -214,6 +214,20 @@ void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf)
 }
 EXPORT_SYMBOL(__drm_printfn_err);
 
+void __drm_printfn_line(struct drm_printer *p, struct va_format *vaf)
+{
+	unsigned int counter = ++p->line.counter;
+	const char *prefix = p->prefix ?: "";
+	const char *pad = p->prefix ? " " : "";
+
+	if (p->line.series)
+		drm_printf(p->arg, "%s%s%u.%u: %pV",
+			   prefix, pad, p->line.series, counter, vaf);
+	else
+		drm_printf(p->arg, "%s%s%u: %pV", prefix, pad, counter, vaf);
+}
+EXPORT_SYMBOL(__drm_printfn_line);
+
 /**
  * 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 089950ad8681..f4d9b98d7909 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -176,7 +176,13 @@ struct drm_printer {
 	void (*puts)(struct drm_printer *p, const char *str);
 	void *arg;
 	const char *prefix;
-	enum drm_debug_category category;
+	union {
+		enum drm_debug_category category;
+		struct {
+			unsigned short series;
+			unsigned short counter;
+		} line;
+	};
 };
 
 void __drm_printfn_coredump(struct drm_printer *p, struct va_format *vaf);
@@ -186,6 +192,7 @@ 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_dbg(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf);
+void __drm_printfn_line(struct drm_printer *p, struct va_format *vaf);
 
 __printf(2, 3)
 void drm_printf(struct drm_printer *p, const char *f, ...);
@@ -357,6 +364,65 @@ static inline struct drm_printer drm_err_printer(struct drm_device *drm,
 	return p;
 }
 
+/**
+ * drm_line_printer - construct a &drm_printer that prefixes outputs with line numbers
+ * @p: the &struct drm_printer which actually generates the output
+ * @prefix: optional output prefix, or NULL for no prefix
+ * @series: optional unique series identifier, or 0 to omit identifier in the output
+ *
+ * This printer can be used to increase the robustness of the captured output
+ * to make sure we didn't lost any intermediate lines of the output. Helpful
+ * while capturing some crash data.
+ *
+ * Example 1::
+ *
+ *	void crash_dump(struct drm_device *drm)
+ *	{
+ *		static unsigned short id;
+ *		struct drm_printer p = drm_err_printer(drm, "crash");
+ *		struct drm_printer lp = drm_line_printer(&p, "dump", ++id);
+ *
+ *		drm_printf(&lp, "foo");
+ *		drm_printf(&lp, "bar");
+ *	}
+ *
+ * Above code will print into the dmesg something like::
+ *
+ *	[ ] 0000:00:00.0: [drm] *ERROR* crash dump 1.1: foo
+ *	[ ] 0000:00:00.0: [drm] *ERROR* crash dump 1.2: bar
+ *
+ * Example 2::
+ *
+ *	void line_dump(struct device *dev)
+ *	{
+ *		struct drm_printer p = drm_info_printer(dev);
+ *		struct drm_printer lp = drm_line_printer(&p, NULL, 0);
+ *
+ *		drm_printf(&lp, "foo");
+ *		drm_printf(&lp, "bar");
+ *	}
+ *
+ * Above code will print::
+ *
+ *	[ ] 0000:00:00.0: [drm] 1: foo
+ *	[ ] 0000:00:00.0: [drm] 2: bar
+ *
+ * RETURNS:
+ * The &drm_printer object
+ */
+static inline struct drm_printer drm_line_printer(struct drm_printer *p,
+						  const char *prefix,
+						  unsigned short series)
+{
+	struct drm_printer lp = {
+		.printfn = __drm_printfn_line,
+		.arg = p,
+		.prefix = prefix,
+		.line = { .series = series, },
+	};
+	return lp;
+}
+
 /*
  * struct device based logging
  *
-- 
2.43.0