[RFC] drm/print: Introduce drm_line_printer

[Michal Wajdeczko]

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 at intel.com>
---
 drivers/gpu/drm/drm_print.c |  9 +++++++++
 include/drm/drm_print.h     | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index cf2efb44722c..d6fb50d3407a 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -214,6 +214,15 @@ 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 line = (uintptr_t)(++p->prefix);
+	struct drm_printer *dp = p->arg;
+
+	drm_printf(dp, "%u: %pV", line, 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..58cc73c53853 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -186,6 +186,7 @@ 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 +358,42 @@ 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
+ * @dp: the &struct drm_printer which actually generates 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.
+ *
+ * For example::
+ *
+ *	void crash_dump(struct drm_device *drm)
+ *	{
+ *		struct drm_printer dp = drm_err_printer(drm, "crash");
+ *		struct drm_printer lp = drm_line_printer(&dp);
+ *
+ *		drm_printf(&lp, "foo");
+ *		drm_printf(&lp, "bar");
+ *	}
+ *
+ * Above code will print into the dmesg something like::
+ *
+ *	[ ] 0000:00:00.0: [drm] *ERROR* crash 1: foo
+ *	[ ] 0000:00:00.0: [drm] *ERROR* crash 2: bar
+ *
+ * RETURNS:
+ * The &drm_printer object
+ */
+static inline struct drm_printer drm_line_printer(struct drm_printer *dp)
+{
+	struct drm_printer lp = {
+		.printfn = __drm_printfn_line,
+		.arg = dp,
+	};
+	return lp;
+}
+
 /*
  * struct device based logging
  *
-- 
2.43.0