linux-kernel - Re: [PATCH v1 00/17] tee: Use bus callbacks instead of driver callbacks

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Message-ID: <ayebinxqpcnl7hpa35ytrudiy7j75u5bdk3enlirkp5pevppeg@6mx6a5fwymwf>
Date: Tue, 16 Dec 2025 12:08:38 +0100
From: Uwe Kleine-König <u.kleine-koenig@...libre.com>
To: Sumit Garg <sumit.garg@....qualcomm.com>
Cc: Sumit Garg <sumit.garg@...nel.org>, 
	Jens Wiklander <jens.wiklander@...aro.org>, Olivia Mackall <olivia@...enic.com>, 
	Herbert Xu <herbert@...dor.apana.org.au>, Clément Léger <clement.leger@...tlin.com>, 
	Alexandre Belloni <alexandre.belloni@...tlin.com>, Ard Biesheuvel <ardb@...nel.org>, 
	Maxime Coquelin <mcoquelin.stm32@...il.com>, Alexandre Torgue <alexandre.torgue@...s.st.com>, 
	Ilias Apalodimas <ilias.apalodimas@...aro.org>, Jan Kiszka <jan.kiszka@...mens.com>, 
	Sudeep Holla <sudeep.holla@....com>, Christophe JAILLET <christophe.jaillet@...adoo.fr>, 
	Michael Chan <michael.chan@...adcom.com>, Pavan Chebbi <pavan.chebbi@...adcom.com>, 
	Rafał Miłecki <zajec5@...il.com>, James Bottomley <James.Bottomley@...senpartnership.com>, 
	Jarkko Sakkinen <jarkko@...nel.org>, Mimi Zohar <zohar@...ux.ibm.com>, 
	David Howells <dhowells@...hat.com>, Paul Moore <paul@...l-moore.com>, 
	James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, 
	Peter Huewe <peterhuewe@....de>, op-tee@...ts.trustedfirmware.org, linux-kernel@...r.kernel.org, 
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	Cristian Marussi <cristian.marussi@....com>, arm-scmi@...r.kernel.org, netdev@...r.kernel.org, 
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	linux-security-module@...r.kernel.org, Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH v1 00/17] tee: Use bus callbacks instead of driver
 callbacks

Hello,

On Tue, Dec 16, 2025 at 01:08:38PM +0530, Sumit Garg wrote:
> On Mon, Dec 15, 2025 at 3:02 PM Uwe Kleine-König
> <u.kleine-koenig@...libre.com> wrote:
> > On Mon, Dec 15, 2025 at 04:54:11PM +0900, Sumit Garg wrote:
> > > Feel free to make the tee_bus_type private as the last patch in the series
> > > such that any followup driver follows this clean approach.
> >
> > There is a bit more to do for that than I'm willing to invest. With my
> > patch series applied `tee_bus_type` is still used in
> > drivers/tee/optee/device.c and drivers/tee/tee_core.c.
> 
> Oh I see, I guess we need to come with some helpers around device
> register/unregister from TEE subsystem as well. Let's plan that for a
> followup patch-set, I don't want this patch-set to be bloated more.

Don't consider me in for that. But it sounds like a nice addition.

> > Maybe it's
> > sensible to merge these two files into a single one.
> 
> It's not possible as the design for TEE bus is to have TEE
> implementation drivers like OP-TEE, AMD-TEE, TS-TEE, QTEE and so on to
> register devices on the bus.

So only OP-TEE uses the bus for devices and the other *-TEE don't. Also
sounds like something worth to be fixed.

> > The things I wonder about additionally are:
> >
> >  - if CONFIG_OPTEE=n and CONFIG_TEE=y|m the tee bus is only used for
> >    drivers but not devices.
> 
> Yeah since the devices are rather added by the TEE implementation driver.
> 
> >
> >  - optee_register_device() calls device_create_file() on
> >    &optee_device->dev after device_register(&optee_device->dev).
> >    (Attention half-knowledge!) I think device_create_file() should not
> >    be called on an already registered device (or you have to send a
> >    uevent afterwards). This should probably use type attribute groups.
> >    (Or the need_supplicant attribute should be dropped as it isn't very
> >    useful. This would maybe be considered an ABI change however.)
> 
> The reasoning for this attribute should be explained by commit:
> 7269cba53d90 ("tee: optee: Fix supplicant based device enumeration").
> In summary it's due to a weird dependency for devices we have with the
> user-space daemon: tee-supplicant.

From reading that once I don't understand it. (But no need to explain
:-)

Still the file should better be added before device_add() is called.

> >  - Why does optee_probe() in drivers/tee/optee/smc_abi.c unregister all
> >    optee devices in its error path (optee_unregister_devices())?
> 
> This is mostly to take care of if any device got registered before the
> failure occured. Let me know if you have a better way to address that.

Without understanding the tee stuff, I'd say: Don't bother and only undo
the things that probe did before the failure.

Best regards
Uwe

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