[PATCH] driver: implement dev_err_probe()

[Ahmad Fatoum]

The function like it's Linux equivalent is meant to be used during
driver probe whenever an error occurs that would lead to aborting the
probe. This allows moving EPROBE_DEFER checks out of drivers and
in future could allow selectively compiling out only error probe
messages, as they are mainly interesting during bring up.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 drivers/base/driver.c  | 49 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/printk.h | 12 +++++++++++
 2 files changed, 61 insertions(+)

diff --git a/drivers/base/driver.c b/drivers/base/driver.c
index 3b22a95e174c..e3615fcd0630 100644
--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c
@@ -10,6 +10,8 @@
  * @brief barebox's driver model, and devinfo command
  */
 
+#define dev_err_probe dev_err_probe
+
 #include <common.h>
 #include <command.h>
 #include <deep-probe.h>
@@ -535,3 +537,50 @@ const void *device_get_match_data(struct device_d *dev)
 
 	return NULL;
 }
+
+/**
+ * dev_err_probe - probe error check and log helper
+ * @loglevel: log level configured in source file
+ * @dev: the pointer to the struct device
+ * @err: error value to test
+ * @fmt: printf-style format string
+ * @...: arguments as specified in the format string
+ *
+ * This helper implements common pattern present in probe functions for error
+ * checking: print debug or error message depending if the error value is
+ * -EPROBE_DEFER and propagate error upwards.
+ * In case of -EPROBE_DEFER it sets also defer probe reason, which can be
+ * checked later by reading devices_deferred debugfs attribute.
+ * It replaces code sequence::
+ *
+ * 	if (err != -EPROBE_DEFER)
+ * 		dev_err(dev, ...);
+ * 	else
+ * 		dev_dbg(dev, ...);
+ * 	return err;
+ *
+ * with::
+ *
+ * 	return dev_err_probe(dev, err, ...);
+ *
+ * Returns @err.
+ *
+ */
+int dev_err_probe(const struct device_d *dev, int err, const char *fmt, ...);
+int dev_err_probe(const struct device_d *dev, int err, const char *fmt, ...)
+{
+	struct va_format vaf;
+	va_list args;
+
+	va_start(args, fmt);
+	vaf.fmt = fmt;
+	vaf.va = &args;
+
+	dev_printf(err == -EPROBE_DEFER ? MSG_DEBUG : MSG_ERR,
+		   dev, "error %pe: %pV", ERR_PTR(err), &vaf);
+
+	va_end(args);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(dev_err_probe);
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 3f370adb90ec..212041927251 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -74,6 +74,18 @@ static inline int pr_print(int level, const char *format, ...)
 #define dev_vdbg(dev, format, arg...)		\
 	__dev_printf(8, (dev) , format , ## arg)
 
+#if LOGLEVEL >= MSG_ERR
+int dev_err_probe(const struct device_d *dev, int err, const char *fmt, ...)
+	__attribute__ ((format(__printf__, 3, 4)));
+#elif !defined(dev_err_probe)
+static int dev_err_probe(const struct device_d *dev, int err, const char *fmt, ...)
+	__attribute__ ((format(__printf__, 3, 4)));
+static inline int dev_err_probe(const struct device_d *dev, int err, const char *fmt, ...)
+{
+	return err;
+}
+#endif
+
 #define __pr_printk(level, format, args...) \
 	({	\
 		(level) <= LOGLEVEL ? pr_print((level), (format), ##args) : 0; \
-- 
2.30.2