linux-kernel - Re: [RESEND PATCH v5 2/5] driver core: add deferring probe reason to devices

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Date:   Wed, 24 Jun 2020 14:34:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andrzej Hajda <a.hajda@...sung.com>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        andy.shevchenko@...il.com, Mark Brown <broonie@...nel.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>
Subject: Re: [RESEND PATCH v5 2/5] driver core: add deferring probe reason to
 devices_deferred property

On Wed, Jun 24, 2020 at 01:41:24PM +0200, 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@...sung.com>
> Reviewed-by: Mark Brown <broonie@...nel.org>
> Reviewed-by: Javier Martinez Canillas <javierm@...hat.com>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
> ---
>  drivers/base/base.h |  3 +++
>  drivers/base/core.c | 10 ++++++----
>  drivers/base/dd.c   | 21 ++++++++++++++++++++-
>  3 files changed, 29 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index 95c22c0f9036..93ef1c2f4c1f 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_msg;
>  	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 __deferred_probe_set_msg(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 ee9da66bff1b..2a96954d5460 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3962,6 +3962,8 @@ define_dev_printk_level(_dev_info, KERN_INFO);
>   *
>   * This helper implements common pattern present in probe functions for error
>   * checking: print message if the error is not -EPROBE_DEFER and propagate it.
> + * In case of -EPROBE_DEFER it sets 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, ...);
> @@ -3977,14 +3979,14 @@ int probe_err(const struct device *dev, int err, const char *fmt, ...)
>  	struct va_format vaf;
>  	va_list args;
>  
> -	if (err == -EPROBE_DEFER)
> -		return err;
> -
>  	va_start(args, fmt);
>  	vaf.fmt = fmt;
>  	vaf.va = &args;
>  
> -	dev_err(dev, "error %d: %pV", err, &vaf);
> +	if (err == -EPROBE_DEFER)
> +		__deferred_probe_set_msg(dev, &vaf);
> +	else
> +		dev_err(dev, "error %d: %pV", err, &vaf);
>  
>  	va_end(args);
>  
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 9a1d940342ac..f44d26454b6a 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_msg);
> +		dev->p->deferred_probe_msg = NULL;
>  	}
>  	mutex_unlock(&deferred_probe_mutex);
>  }
> @@ -211,6 +214,21 @@ void device_unblock_probing(void)
>  	driver_deferred_probe_trigger();
>  }
>  
> +/*
> + * __deferred_probe_set_msg() - Set defer probe reason message for device
> + */
> +void __deferred_probe_set_msg(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_msg);
> +	dev->p->deferred_probe_msg = kasprintf(GFP_KERNEL, "%s: %pV", drv, vaf);

What about the device name?  Don't you also want that?

You want the same format that __dev_printk() outputs, please use that
to be consistant with all other messages that drivers are spitting out.

thanks,

greg k-h