linux-kernel - Re: [PATCH] bus: subsys: propagate errors from subsys interface's ->add

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Date:	Thu, 30 Jul 2015 01:01:21 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, pi-cheng.chen@...aro.org
Subject: Re: [PATCH] bus: subsys: propagate errors from subsys interface's ->add_dev()

On Wednesday, July 29, 2015 02:19:16 PM Greg KH wrote:
> On Fri, Jun 26, 2015 at 02:32:47PM +0530, Viresh Kumar wrote:
> > ->add_dev() may fail and the error returned from it can be useful for
> > the caller.
> > 
> > For example, if some of the resources aren't ready yet and -EPROBE_DEFER
> > is returned from ->add_dev(), then the owner of 'struct
> > subsys_interface' may want to try probing again at a later point of
> > time. And that requires a proper return value from ->add_dev().
> > 
> > Also, if we hit an error while registering subsys_interface, then we
> > should stop proceeding further and rollback whatever has been done until
> > then. Break part of subsys_interface_unregister() into another routine,
> > which lets us call ->remove_dev() for all devices for which ->add_dev()
> > is already called.
> > 
> > Cc: 3.3+ <stable@...r.kernel.org> # 3.3+
> > Fixes: ca22e56debc5 ("driver-core: implement 'sysdev' functionality for regular devices and buses")
> 
> I don't see how this is a stable bug fix, what is resolved by it that
> doesn't work today?  Is there some code that is expecting this
> functionality that has never been present?
> 
> I'll go queue it up, but I don't think it is -stable material, but feel
> free to change my mind.

There is a small problem with it that I've already pointed out to Viresh.

Namely, while changing subsys_interface_(un)register() to handle return
values from ->add_dev(), it doesn't do the same thing in bus_probe_device()
which I believe it should for consistency at least.

But then, the question is whether or not the probing should fail and
what if device_attach() returns 0 and one of the ->add_dev() callbacks
returns an error.

Thanks,
Rafael

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