linux-kernel - Re: [PATCH v14 3/5] tee: add OP-TEE driver

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Message-ID: <20170124125330.GA30998@jax>
Date:   Tue, 24 Jan 2017 13:53:31 +0100
From:   Jens Wiklander <jens.wiklander@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 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.

Thanks for the help with this review.

Jens