linux-kernel - Re: [tpmdd-devel] [RFC PATCH 1/2] tee: generic TEE subsystem

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Date:	Mon, 20 Apr 2015 18:05:45 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Jens Wiklander <jens.wiklander@...aro.org>,
	valentin.manea@...wei.com, devicetree@...r.kernel.org,
	javier@...igon.com, emmanuel.michel@...com,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	jean-michel.delorme@...com, tpmdd-devel@...ts.sourceforge.net,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [tpmdd-devel] [RFC PATCH 1/2] tee: generic TEE subsystem

On Mon, Apr 20, 2015 at 09:56:48AM -0600, Jason Gunthorpe wrote:
> On Mon, Apr 20, 2015 at 04:54:32PM +0200, Greg Kroah-Hartman wrote:
> > On Sun, Apr 19, 2015 at 11:08:00PM -0600, Jason Gunthorpe wrote:
> > > I still suspect the expected way to write a new mid layer is to create
> > > your own struct device and not rely on misc_device,
> > 
> > Yes, that is the way.  You can not use misc_device for anything other
> > than creating the char node that your driver can use through the fileops
> > you pass to it.
> > 
> > Do not use a misc_device to create sysfs files for, or anything else, it
> > will be wrong and racy, as you have pointed out.
> 
> Thanks!
> 
> Can you quickly comment on when a misc device should be used compared to
> alloc_chrdev_region & cdev_add ?

If you need more than one character device node, don't use a misc
device.  If you only need one, and nothing "special" or "fancy", and
don't want to put sysfs attribute files on your device, then use a misc
device.

thanks,

greg k-h
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