linux-kernel - Re: [PATCH v7 01/20] driver core: handle -EPROBE_DEFER from bus

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Date:	Fri, 16 Oct 2015 23:51:33 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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>,
	Mark Brown <broonie@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-arm-kernel@...ts.infradead.org,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	devicetree@...r.kernel.org,
	Russell King <rmk+kernel@....linux.org.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-acpi@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v7 01/20] driver core: handle -EPROBE_DEFER from
 bus_type.match()

On Tue, Sep 29, 2015 at 11:10:39AM +0200, 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);

This is going to start to cause warnings where there were previously
none, which isn't going to be a good idea.  It's completly normal for a
bus to not match a device, let's not be noisy for no good reason, unless
you are going to deal with all of the confused user emails?

You do this a bunch in this patch, please don't.

thanks,

greg k-h
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