linux-kernel - Re: [PATCH 1/7] platform_device: better support builtin boilerplate avoidance

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Message-ID: <556F0A17.2050306@windriver.com>
Date:	Wed, 3 Jun 2015 10:07:19 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/7] platform_device: better support builtin boilerplate
 avoidance

On 15-06-02 05:19 AM, Linus Walleij wrote:
> On Thu, May 28, 2015 at 2:50 AM, Paul Gortmaker
> <paul.gortmaker@...driver.com> wrote:
>> [Re: [PATCH 1/7] platform_device: better support builtin boilerplate avoidance] On 12/05/2015 (Tue 13:46) Linus Walleij wrote:
>>
>>> This does not inhibit probe() and remove() to be
>>> triggered from sysfs does it?
>>>
>>> What is needed on builtin drivers is to set
>>> .suppress_bind_attrs = true on the struct device_driver
>>> so that we inhibit the creation of sysfs files to probe
>>> and remove the driver by operator intervention.
>>
>> Is this needed?  I think we will break existing use cases if we do this.
>>
>> For example, I have IGB as built-in, but I can still unbind one of the
>> four devices and make it available for PCI pass through to KVM with:
>>
>> echo "0000:0a:00.1" > /sys/bus/pci/drivers/igb/unbind
>> echo "0000:0a:00.1" > /sys/bus/pci/drivers/pci-stub/bind
> 
> Aha PCI device which noone else is dependent on, I guess
> it's true.
> 
> I think we have a problem as to what "builtin" really means.

Well, people have had trouble with what "is" means before, so
I guess it is possible.  However, I think here it is pretty clear
that builtin means a Kconfig which is "y" and where "m" is not a
possible selection.

> For example if this is a builtin regulator, clock, GPIO, DMA etc
> driver, we want to suppress the binding/unbinding from userspace
> too, since these drivers provide resources to others and
> if you unbind them, nasty things happen. Unbinding/rebinding
> is fine as long as noone else depend on you. However for
> a large number of builtins, that is the case :P

So, to summarize:

1) Currently drivers can unbind that really should not do so.

2) This is not a new issue, nor is it introduced by this series.

3) We can't set policy based on built in vs modular; the only
   sane thing appears to be to let the driver decide itself.

Paul.
--

> 
> Yours,
> Linus Walleij
> 
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