Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Grygorii Strashko]

On 26/06/2020 13:01, Andrzej Hajda wrote:
> /sys/kernel/debug/devices_deferred property contains list of deferred devices.
> This list does not contain reason why the driver deferred probe, the patch
> improves it.
> The natural place to set the reason is probe_err function introduced recently,
> ie. if probe_err will be called with -EPROBE_DEFER instead of printk the message
> will be attached to deferred device and printed when user read devices_deferred
> property.
>
> Signed-off-by: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> Reviewed-by: Mark Brown <broonie@xxxxxxxxxx>
> Reviewed-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> ---
>   drivers/base/base.h |  3 +++
>   drivers/base/core.c |  8 ++++++--
>   drivers/base/dd.c   | 23 ++++++++++++++++++++++-
>   3 files changed, 31 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index 95c22c0f9036..6954fccab3d7 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -93,6 +93,7 @@ struct device_private {
>   	struct klist_node knode_class;
>   	struct list_head deferred_probe;
>   	struct device_driver *async_driver;
> +	char *deferred_probe_reason;
>   	struct device *device;
>   	u8 dead:1;
>   };
> @@ -134,6 +135,8 @@ extern void device_release_driver_internal(struct device *dev,
>   extern void driver_detach(struct device_driver *drv);
>   extern int driver_probe_device(struct device_driver *drv, struct device *dev);
>   extern void driver_deferred_probe_del(struct device *dev);
> +extern void device_set_deferred_probe_reson(const struct device *dev,
> +					    struct va_format *vaf);
>   static inline int driver_match_device(struct device_driver *drv,
>   				      struct device *dev)
>   {
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 3a827c82933f..fee047f03681 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3963,6 +3963,8 @@ define_dev_printk_level(_dev_info, KERN_INFO);
>    * 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, ...);
> @@ -3984,10 +3986,12 @@ int dev_err_probe(const struct device *dev, int err, const char *fmt, ...)
>   	vaf.fmt = fmt;
>   	vaf.va = &args;
>   
> -	if (err != -EPROBE_DEFER)
> +	if (err != -EPROBE_DEFER) {
>   		dev_err(dev, "error %d: %pV", err, &vaf);
> -	else
> +	} else {
> +		device_set_deferred_probe_reson(dev, &vaf);
>   		dev_dbg(dev, "error %d: %pV", err, &vaf);
> +	}
>   
>   	va_end(args);
>   
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 9a1d940342ac..dd5683b61f74 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -27,6 +27,7 @@
>   #include <linux/async.h>
>   #include <linux/pm_runtime.h>
>   #include <linux/pinctrl/devinfo.h>
> +#include <linux/slab.h>
>   
>   #include "base.h"
>   #include "power/power.h"
> @@ -136,6 +137,8 @@ void driver_deferred_probe_del(struct device *dev)
>   	if (!list_empty(&dev->p->deferred_probe)) {
>   		dev_dbg(dev, "Removed from deferred list\n");
>   		list_del_init(&dev->p->deferred_probe);
> +		kfree(dev->p->deferred_probe_reason);
> +		dev->p->deferred_probe_reason = NULL;
>   	}
>   	mutex_unlock(&deferred_probe_mutex);
>   }
> @@ -211,6 +214,23 @@ void device_unblock_probing(void)
>   	driver_deferred_probe_trigger();
>   }
>   
> +/**
> + * device_set_deferred_probe_reson() - Set defer probe reason message for device
> + * @dev: the pointer to the struct device
> + * @vaf: the pointer to va_format structure with message
> + */
> +void device_set_deferred_probe_reson(const struct device *dev, struct va_format *vaf)
> +{
> +	const char *drv = dev_driver_string(dev);
> +
> +	mutex_lock(&deferred_probe_mutex);
> +
> +	kfree(dev->p->deferred_probe_reason);
> +	dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s: %pV", drv, vaf);
> +
> +	mutex_unlock(&deferred_probe_mutex);
> +}
> +
>   /*
>    * deferred_devs_show() - Show the devices in the deferred probe pending list.
>    */
> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s, void *data)
>   	mutex_lock(&deferred_probe_mutex);
>   
>   	list_for_each_entry(curr, &deferred_probe_pending_list, deferred_probe)
> -		seq_printf(s, "%s\n", dev_name(curr->device));
> +		seq_printf(s, "%s\t%s", dev_name(curr->device),
> +			   curr->device->p->deferred_probe_reason ?: "\n");
>   
>   	mutex_unlock(&deferred_probe_mutex);
>   

Sry, may be i missing smth, but shouldn't it be optional
(CONFIG_DEBUG_FS is probably too generic).

--
Best regards,
grygorii