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Date:   Wed, 25 Jan 2017 11:02:53 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jens Wiklander <jens.wiklander@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Wei Xu <xuwei5@...ilicon.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>, valentin.manea@...wei.com,
        jean-michel.delorme@...com, emmanuel.michel@...com,
        javier@...igon.com,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Mark Rutland <mark.rutland@....com>,
        Michal Simek <michal.simek@...inx.com>,
        Rob Herring <robh+dt@...nel.org>,
        Will Deacon <will.deacon@....com>, Nishanth Menon <nm@...com>,
        "Andrew F . Davis" <afd@...com>, broonie@...nel.org,
        scott.branden@...adcom.com
Subject: Re: [PATCH v14 3/5] tee: add OP-TEE driver

On Wed, Jan 25, 2017 at 10:47:45AM +0100, Jens Wiklander wrote:
> On Tue, Jan 24, 2017 at 01:53:30PM +0100, Jens Wiklander wrote:
> > On Mon, Jan 23, 2017 at 05:16:15PM +0100, Arnd Bergmann wrote:
> > > On Monday, January 23, 2017 10:08:53 AM CET Jens Wiklander wrote:
> > > > On Fri, Jan 20, 2017 at 05:57:51PM +0100, Arnd Bergmann wrote:
> > > > > On Thursday, January 19, 2017 3:56:23 PM CET Jens Wiklander wrote:
> > > > > > On Wed, Jan 18, 2017 at 05:28:17PM +0100, Arnd Bergmann wrote:
> > > 
> > > > > > Does the platform devices really need cleaning? I mean
> > > > > > of_platform_default_populate_init() creates a bunch of platform devices
> > > > > > which are just left there even if unused. Here we're doing the same
> > > > > > thing except that we're doing it for a specific node in the DT.
> > > > > 
> > > > > I think it will work if you don't clean them up, but it feels wrong
> > > > > to have a loadable module that creates devices when loaded but doesn't
> > > > > remove them when unloaded.
> > > > > 
> > > > > This could be done differently by having the device creation done in
> > > > > one driver and the the user of that device in another driver, but I
> > > > > think just killing off the device achieves the same in a simpler way.
> > > > 
> > > > I see your point. My final concern here is that with device we got
> > > > entries in sysfs and uevents that could be used to automatically start
> > > > the correct supplicant. Different drivers are likely to require
> > > > different supplicants. Starting the correct supplicant based on uevents
> > > > is a quite elegant solution which I'm not sure how to support when
> > > > skipping devices. Perhaps I could create an object below
> > > > <sysfs>/firmware/tee ?
> > > 
> > > Putting the objects somewhere other than /sys/devices sounds good, yes.
> > > This would also help with TEE implementations that might get probed
> > > differently.
> > > 
> > > I think the natural place would be /sys/class/tee/, as we normally
> > > require something in /sys/class anyway to support the character
> > > device.
> > > 
> > > /sys/firmware/tee/ sounds less fitting, as there other TEE implementations
> > > are not necessarily firmware based, as you point out. 
> > > /sys/firmware/op-tee certainly makes sense for anything that is specific
> > > to OP-TEE in particular, while /sys/class/tee would be for anything
> > > that uses the ioctl interface. This part is particularly important to
> > > get right from the start, just like the ioctls themselves we can't make
> > > incompatible changes here later once there are users relying on the
> > > upstream kernel interfaces.
> > 
> > /sys/class/tee/ sounds good, I'll use that. It's more or less what we
> > also have today.
> 
> I'm sorry, it seems a struct device has to be used in order to put stuff
> under /sys/class/tee/. Or am I missing something?

Nope, that is correct.

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