linux-kernel - Re: [REPOST][PATCH 1/2] driver core: Add new device_driver flag to allow binding via sysfs only

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Date:	Thu, 19 Dec 2013 14:32:23 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Scott Wood <scottwood@...escale.com>
Cc:	Stuart Yoder <stuart.yoder@...escale.com>,
	Kim Phillips <kim.phillips@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Bharat.Bhushan@...escale.com" <Bharat.Bhushan@...escale.com>,
	"christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"a.motakis@...tualopensystems.com" <a.motakis@...tualopensystems.com>,
	"agraf@...e.de" <agraf@...e.de>,
	Varun Sethi <Varun.Sethi@...escale.com>
Subject: Re: [REPOST][PATCH 1/2] driver core: Add new device_driver flag to
 allow binding via sysfs only

On Thu, Dec 19, 2013 at 04:15:03PM -0600, Scott Wood wrote:
> On Thu, 2013-12-19 at 13:43 -0800, Greg Kroah-Hartman wrote:
> > On Thu, Dec 19, 2013 at 09:06:21PM +0000, Stuart Yoder wrote:
> > > 
> > > 
> > > > -----Original Message-----
> > > > From: Greg Kroah-Hartman [mailto:gregkh@...uxfoundation.org]
> > > > Sent: Thursday, December 19, 2013 2:34 PM
> > > > To: Wood Scott-B07421
> > > > Cc: Kim Phillips; linux-kernel@...r.kernel.org; kvm@...r.kernel.org;
> > > > Bhushan Bharat-R65777; Yoder Stuart-B08248; christoffer.dall@...aro.org;
> > > > alex.williamson@...hat.com; a.motakis@...tualopensystems.com;
> > > > agraf@...e.de; Sethi Varun-B16395
> > > > Subject: Re: [REPOST][PATCH 1/2] driver core: Add new device_driver flag
> > > > to allow binding via sysfs only
> > > > 
> > > > No.  But you can use bind/unbind along with the existing new_id file to
> > > > get what you want today.
> > > 
> > > Yes, but that only works for PCI.
> > 
> > No, not only PCI.
> > 
> > > There is no such concept for platform drivers.
> > 
> > Then fix that.
> 
> We've already explained why that would be bad.

No you haven't, or if you have, my squirrel-brain doesn't remember it...

> > Or make your device not be a platform device, odds are that's the better
> > solution in the end, right?
> 
> How would that solve anything?  We'd just be talking about there not
> being such a mechanism for the device tree "bus" instead.

Nope, you could add it there, like PCI and other busses have.

> > > > I don't like this patch as we are adding lots of special and odd logic
> > > > to the core, for use by almost no one, which ensures that it will never
> > > > get tested, and will probably get broken in some subtle way in the
> > > > future.
> > > 
> > > It certainly will be used by users of vfio-platform.
> > > 
> > > Here is the problem-- the new platform device "match_any_dev" mechanism
> > > in patch 2 of this series is not going to work without "sysfs_bind_only".
> > > A platform driver that just sets "match_any_dev" will grab any or all 
> > > platform devices during normal bus probing.
> > 
> > No it will not, it will fail in the probe function as it knows to not
> > grab the device, just like any driver for other busses that say it can
> > "handle all Intel PCI devices" and the like.
> 
> How will it "know not to grab the device"?  The knowledge of whether the
> binding was explicitly requested or not does not get passed through to
> the probe function.

Nor should it, as a driver should not know, nor care about this.

It's up to the BUS to handle this if it really wants to, and I'm afraid
that I really am not convinced that the driver core needs to handle it
either.

But again, as you don't have anything that could actually use this code
that is mergable, it's a totally moot point, sorry.

greg k-h
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