Re: [PATCH v14 3/5] tee: add OP-TEE driver - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Jens Wiklander <jens.wiklander@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>, Olof Johansson <olof@lixom.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Wei Xu <xuwei5@hisilicon.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
	Al Viro <viro@zeniv.linux.org.uk>,
	valentin.manea@huawei.com, jean-michel.delorme@st.com,
	emmanuel.michel@st.com, javier@javigon.com,
	Jason Gunthorpe <jgunthorpe@obsidianresearch.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Michal Simek <michal.simek@xilinx.com>,
	Rob Herring <robh+dt@kernel.org>,
	Will Deacon <will.deacon@arm.com>, Nishanth Menon <nm@ti.com>,
	"Andrew F . Davis" <afd@ti.com>,
	broonie@kernel.org, scott.branden@broadcom.com
Subject: Re: [PATCH v14 3/5] tee: add OP-TEE driver
Date: Wed, 25 Jan 2017 11:02:53 +0100	[thread overview]
Message-ID: <20170125100252.GA8889@kroah.com> (raw)
In-Reply-To: <20170125094744.GA7121@jax>

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.