linux-kernel - Re: [PATCH v6 01/22] driver core: handle -EPROBE_DEFER from bus

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Date:	Thu, 22 Oct 2015 03:00:27 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:	linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-arm-kernel@...ts.infradead.org,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	devicetree@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-acpi@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v6 01/22] driver core: handle -EPROBE_DEFER from bus_type.match()

On Monday, September 21, 2015 04:02:41 PM Tomeu Vizoso wrote:
> Lets implementations of the match() callback in struct bus_type to
> return errors and if it's -EPROBE_DEFER then queue the device for
> deferred probing.
> 
> This is useful to buses such as AMBA in which devices are registered
> before their matching information can be retrieved from the HW
> (typically because a clock driver hasn't probed yet).
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> ---
> 
> 
>  drivers/base/dd.c      | 24 ++++++++++++++++++++++--
>  include/linux/device.h |  2 +-
>  2 files changed, 23 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index be0eb4639128..7dc04ee81c8b 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -488,6 +488,7 @@ static int __device_attach_driver(struct device_driver *drv, void *_data)
>  	struct device_attach_data *data = _data;
>  	struct device *dev = data->dev;
>  	bool async_allowed;
> +	int ret;
>  
>  	/*
>  	 * Check if device has already been claimed. This may
> @@ -498,8 +499,17 @@ static int __device_attach_driver(struct device_driver *drv, void *_data)
>  	if (dev->driver)
>  		return -EBUSY;
>  
> -	if (!driver_match_device(drv, dev))
> +	ret = driver_match_device(drv, dev);
> +	if (!ret)
>  		return 0;
> +	else if (ret < 0) {
> +		if (ret == -EPROBE_DEFER) {
> +			dev_dbg(dev, "Device match requests probe deferral\n");
> +			driver_deferred_probe_add(dev);
> +		} else
> +			dev_warn(dev, "Bus failed to match device: %d", ret);
> +		return ret;
> +	}

The code below was reachable if an error was returned from driver_match_device()
before this patch.  What's the reason for changing that?

Shouldn't the code here really be:

	ret = driver_match_device(drv, dev);
	if (!ret)
		return 0;

	if (ret == -EPROBE_DEFER) {
		driver_deferred_probe_add(dev);
		return ret;
	}

>  	async_allowed = driver_allows_async_probing(drv);
>  
> @@ -619,6 +629,7 @@ void device_initial_probe(struct device *dev)
>  static int __driver_attach(struct device *dev, void *data)
>  {
>  	struct device_driver *drv = data;
> +	int ret;
>  
>  	/*
>  	 * Lock device and try to bind to it. We drop the error
> @@ -630,8 +641,17 @@ static int __driver_attach(struct device *dev, void *data)
>  	 * is an error.
>  	 */
>  
> -	if (!driver_match_device(drv, dev))
> +	ret = driver_match_device(drv, dev);
> +	if (!ret)
> +		return 0;
> +	else if (ret < 0) {
> +		if (ret == -EPROBE_DEFER) {
> +			dev_dbg(dev, "Device match requests probe deferral\n");
> +			driver_deferred_probe_add(dev);
> +		} else
> +			dev_warn(dev, "Bus failed to match device: %d", ret);
>  		return 0;

Same comment here, plus why do we return 0 at this point?

> +	}
>  
>  	if (dev->parent)	/* Needed for USB */
>  		device_lock(dev->parent);
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 5d7bc6349930..8e7b806f0744 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -70,7 +70,7 @@ extern void bus_remove_file(struct bus_type *, struct bus_attribute *);
>   * @dev_groups:	Default attributes of the devices on the bus.
>   * @drv_groups: Default attributes of the device drivers on the bus.
>   * @match:	Called, perhaps multiple times, whenever a new device or driver
> - *		is added for this bus. It should return a nonzero value if the
> + *		is added for this bus. It should return a positive value if the
>   *		given device can be handled by the given driver.
>   * @uevent:	Called when a device is added, removed, or a few other things
>   *		that generate uevents to add the environment variables.
> 

Thanks,
Rafael

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