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

[Ahmad Fatoum]

On 08.07.22 11:41, Johannes Zink wrote:
> 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>

Reviewed-by: Ahmad Fatoum <a.fatoum 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;
>  }


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