linux-kernel - Re: [linux-sunxi] Re: [PATCH 1/2] Initial support for Allwinner's Security ID fuses

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Date:	Wed, 17 Jul 2013 09:17:58 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Oliver Schinagl <oliver+list@...inagl.nl>,
	linux-sunxi@...glegroups.com, arnd@...db.de,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	andy.shevchenko@...il.com, linux@....linux.org.uk,
	linus.walleij@...aro.org, Oliver Schinagl <oliver@...inagl.nl>
Subject: Re: [linux-sunxi] Re: [PATCH 1/2] Initial support for Allwinner's
 Security ID fuses

On Wed, Jul 17, 2013 at 01:46:50PM +0200, Maxime Ripard wrote:
> On Mon, Jul 15, 2013 at 11:41:07PM -0700, Greg KH wrote:
> > On Mon, Jul 15, 2013 at 11:16:19PM +0200, Oliver Schinagl wrote:
> > > So using these new patches for binary attributes, how can I pass data 
> > > between my driver and the sysfs files using a platform_driver? Or are 
> > > other 'hacks' needed and using the .groups attribute from 
> > > platform_driver->device_driver->groups is really the wrong approach.
> > > 
> > > I did ask around and still haven't figured it out so far, so I do 
> > > apologize if you feel I'm wasting your precious time.
> > 
> > How is the platform device not the same thing that was passed to your
> > probe function?
> 
> One thing I don't get here is why it should be set in the
> platform_driver structure. From my understanding of the device model,
> and since what Oliver is trying to do is exposing a few bytes of memory
> to sysfs, shouldn't the sysfs file be attached to the device instead?

It will be created by the driver core for any device attached to the
driver automatically.

> I mean, here, the sysfs file will be created under something like
> .../drivers/sunxi-sid/eeprom. What happens when you have several
> instances of that driver loaded? I'd expect it to have several sysfs
> files created, one for each instance. So to me, it should be in the
> device structure, not the driver one.

You can't have multiple drivers with the same name loaded (or the same
module loaded multiple times.)  You can have multiple devices for a
single driver, which is what we do all the time.

> Couldn't that be also the reason of Oliver's NULL pointer? If the kobj
> is attached to the platform_driver and not to the platform_device, it
> should definitely get nasty when we try to cast it and retrieve data
> from it (and that would match the different pointers stuff as well.)

No, he's getting a kobject that looks quite different at probe that is
different from when the file callback happens, something is odd here...

greg k-h
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