[PATCH v3] base: driver: print dev_err_probe message on permanent probe deferral

[Johannes Zink]

This stores the probe deferral reason in the device structure.
If a probe is permanently deferred, the last reason is displayed.

Example output on a permanently deferred probe:
  ERROR: imx-pgc-domain0: probe permanently deferred (Failed to get domain's regulator)

Other dev_err_probe outputs are displayed as before.

Signed-off-by: Johannes Zink <j.zink at pengutronix.de>
---
v1 -> v2:
  - improved commit message
  - improved function prototypes
  - improved debug output, device name is displayed once only per
    message
  - reverted removal of MSG_DEBUG output on deferred probe
  - replaced kfree by free
  - removed unnecessary null checks before free
  - fixed several typos
  - fixed compiler warnings
  - fixed coding style issues
v2 -> v3:
  - dropped const from dev_err_probe
  - use xasprintf instead of basprintf: guarantee memory allocation
  - prevent newline within message on permanent deferral
  - removed unnecessary helper functions
  - fixed remaining typos and whitespace changes
  - improved comments
  - reverted removal of kernel doc comment 
  - added example in commit message
---
 drivers/base/driver.c  | 44 +++++++++++++++++++++++++++++++++++-------
 include/driver.h       |  5 +++++
 include/linux/printk.h |  6 +++---
 3 files changed, 45 insertions(+), 10 deletions(-)

diff --git a/drivers/base/driver.c b/drivers/base/driver.c
index 303ca061c..4898e0114 100644
--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c
@@ -283,6 +283,7 @@ void free_device_res(struct device_d *dev)
 	dev->name = NULL;
 	free(dev->unique_name);
 	dev->unique_name = NULL;
+	free(dev->deferred_probe_reason);
 }
 EXPORT_SYMBOL(free_device_res);
 
@@ -333,9 +334,13 @@ static int device_probe_deferred(void)
 		}
 	} while (success);
 
-	list_for_each_entry(dev, &deferred, active)
-		dev_err(dev, "probe permanently deferred\n");
-
+	list_for_each_entry(dev, &deferred, active) {
+		if (dev->deferred_probe_reason)
+			dev_err(dev, "probe permanently deferred (%s)\n",
+				dev->deferred_probe_reason);
+		else
+			dev_err(dev, "probe permanently deferred\n");
+	}
 	return 0;
 }
 late_initcall(device_probe_deferred);
@@ -573,6 +578,24 @@ const void *device_get_match_data(struct device_d *dev)
 	return NULL;
 }
 
+static void device_set_deferred_probe_reason(struct device_d *dev, const struct va_format *vaf)
+{
+	char *reason;
+	char *last_char;
+
+	free(dev->deferred_probe_reason);
+
+	reason = xasprintf("%pV", vaf);
+
+	/* drop newline char at end of reason string */
+	last_char = reason + strlen(reason) - 1;
+
+	if (*last_char == '\n')
+		*last_char = '\0';
+
+	dev->deferred_probe_reason = reason;
+}
+
 /**
  * dev_err_probe - probe error check and log helper
  * @loglevel: log level configured in source file
@@ -584,8 +607,12 @@ const void *device_get_match_data(struct device_d *dev)
  * 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.
+ *
+ * In case of -EPROBE_DEFER it sets the device's deferred_probe_reason attribute,
+ * but does not report an error. The error is recorded and displayed later, if
+ * (and only if) the probe is permanently deferred. For all other error codes,
+ * it just outputs the error along with the formatted message.
+ *
  * It replaces code sequence::
  *
  * 	if (err != -EPROBE_DEFER)
@@ -601,8 +628,8 @@ const void *device_get_match_data(struct device_d *dev)
  * 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, ...)
+int dev_err_probe(struct device_d *dev, int err, const char *fmt, ...);
+int dev_err_probe(struct device_d *dev, int err, const char *fmt, ...)
 {
 	struct va_format vaf;
 	va_list args;
@@ -611,6 +638,9 @@ int dev_err_probe(const struct device_d *dev, int err, const char *fmt, ...)
 	vaf.fmt = fmt;
 	vaf.va = &args;
 
+	if (err == -EPROBE_DEFER)
+		device_set_deferred_probe_reason(dev, &vaf);
+
 	dev_printf(err == -EPROBE_DEFER ? MSG_DEBUG : MSG_ERR,
 		   dev, "error %pe: %pV", ERR_PTR(err), &vaf);
 
diff --git a/include/driver.h b/include/driver.h
index b35b5f397..a89ce7af9 100644
--- a/include/driver.h
+++ b/include/driver.h
@@ -88,6 +88,11 @@ struct device_d {
 	 * when the driver should actually detect client devices
 	 */
 	int     (*detect) (struct device_d *);
+
+	/*
+	 * if a driver probe is deferred, this stores the last error
+	 */
+	char *deferred_probe_reason;
 };
 
 /** @brief Describes a driver present in the system */
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 39523b057..e21e859bf 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -76,12 +76,12 @@ static inline int pr_print(int level, const char *format, ...)
 	__dev_printf(8, (dev) , format , ## arg)
 
 #if LOGLEVEL >= MSG_ERR
-int dev_err_probe(const struct device_d *dev, int err, const char *fmt, ...)
+int dev_err_probe(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, ...)
+static int dev_err_probe(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, ...)
+static inline int dev_err_probe(struct device_d *dev, int err, const char *fmt, ...)
 {
 	return err;
 }
-- 
2.30.2