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Date: Thu, 28 May 2015 09:23:00 -0700
From: Greg KH <gregkh@linuxfoundation.org>
To: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Tal Shorer <tal.shorer@gmail.com>,
        Sasha Levin <sasha.levin@oracle.com>,
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        David Cohen <david.a.cohen@linux.intel.com>,
        Felipe Balbi <balbi@ti.com>, Lu Baolu <baolu.lu@linux.intel.com>
Subject: Re: [PATCH] usb: ulpi: don't register drivers if bus doesn't exist
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On Thu, May 28, 2015 at 11:09:38AM +0530, Sudip Mukherjee wrote:
> On Wed, May 27, 2015 at 08:21:16AM -0700, Greg KH wrote:
> > On Wed, May 27, 2015 at 11:16:34AM -0400, Alan Stern wrote:
> > > On Wed, 27 May 2015, Heikki Krogerus wrote:
> > 
> > Maybe we need to test for this in the driver core, not allowing drivers
> > for busses that are not registered, that might solve the main problem
> > here.  I'll try to look at it tonight.
> may i suggest something like this ?
> buildtest with allmodconfig and allyesconfig on x86_64.
> built and booted on x86.
> 
> 
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index 5005924..95cefa0 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -943,6 +943,7 @@ int bus_register(struct bus_type *bus)
>  	if (retval)
>  		goto bus_groups_fail;
>  
> +	bus->registered = true;
>  	pr_debug("bus: '%s': registered\n", bus->name);
>  	return 0;
>  
> diff --git a/drivers/base/driver.c b/drivers/base/driver.c
> index 4eabfe2..1acae5b 100644
> --- a/drivers/base/driver.c
> +++ b/drivers/base/driver.c
> @@ -150,6 +150,11 @@ int driver_register(struct device_driver *drv)
>  	int ret;
>  	struct device_driver *other;
>  
> +	if (!drv->bus->registered) {
> +		pr_err("Driver %s registration failed. bus not yet registered\n",
> +		       drv->name);
> +		return -ENODEV;
> +	}
>  	BUG_ON(!drv->bus->p);
>  
>  	if ((drv->bus->probe && drv->probe) ||
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 00ac57c..8fe4745 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -126,6 +126,7 @@ struct bus_type {
>  	const struct dev_pm_ops *pm;
>  
>  	const struct iommu_ops *iommu_ops;
> +	bool registered;	/* DON'T TOUCH THIS */

As if anyone ever looks at comments and follows them :)

Anyway, let me look at this some more, I think this needs to go into the
individual buses, not the driver core.  There's a lot more to initialize
than just the driver core for most busses, they should be the ones to
allow a driver to be registered or not, not the driver core, which
shouldn't care.

I have some time on Saturday (very long plane ride), where I'll take a
look at this.

thanks,

greg k-h