Re: [PATCH v2 02/15] firmware: qcom: Add a generic PAS service

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 3/23/26 3:19 PM, Krzysztof Kozlowski wrote:
> On 23/03/2026 14:22, Sumit Garg wrote:
>> On Mon, Mar 16, 2026 at 08:51:16AM +0100, Krzysztof Kozlowski wrote:
>>> On 12/03/2026 07:27, Sumit Garg wrote:
>>>> From: Sumit Garg <sumit.garg@oss.qualcomm.com>
>>>>
>>>> Qcom platforms has the legacy of using non-standard SCM calls
>>>> splintered over the various kernel drivers. These SCM calls aren't
>>>> compliant with the standard SMC calling conventions which is a
>>>> prerequisite to enable migration to the FF-A specifications from Arm.
>>>>
>>>> OP-TEE as an alternative trusted OS to Qualcomm TEE (QTEE) can't
>>>> support these non-standard SCM calls. And even for newer architectures
>>>> with S-EL2 and Hafnium support, QTEE won't be able to support SCM
>>>> calls either with FF-A requirements coming in. And with both OP-TEE
>>>> and QTEE drivers well integrated in the TEE subsystem, it makes further
>>>> sense to reuse the TEE bus client drivers infrastructure.
>>>>
>>>> The added benefit of TEE bus infrastructure is that there is support
>>>> for discoverable/enumerable services. With that client drivers don't
>>>> have to manually invoke a special SCM call to know the service status.
>>>>
>>>> So enable the generic Peripheral Authentication Service (PAS) provided
>>>> by the firmware. It acts as the common layer with different TZ
>>>> backends plugged in whether it's an SCM implementation or a proper
>>>> TEE bus based PAS service implementation.
>>>>
>>>> Signed-off-by: Sumit Garg <sumit.garg@oss.qualcomm.com>
>>>> ---
>>>>  drivers/firmware/qcom/Kconfig          |   8 +
>>>>  drivers/firmware/qcom/Makefile         |   1 +
>>>>  drivers/firmware/qcom/qcom_pas.c       | 298 +++++++++++++++++++++++++
>>>>  drivers/firmware/qcom/qcom_pas.h       |  53 +++++
>>>>  include/linux/firmware/qcom/qcom_pas.h |  41 ++++
>>>>  5 files changed, 401 insertions(+)
>>>>  create mode 100644 drivers/firmware/qcom/qcom_pas.c
>>>>  create mode 100644 drivers/firmware/qcom/qcom_pas.h
>>>>  create mode 100644 include/linux/firmware/qcom/qcom_pas.h
>>>>
>>>> diff --git a/drivers/firmware/qcom/Kconfig b/drivers/firmware/qcom/Kconfig
>>>> index b477d54b495a..8653639d06db 100644
>>>> --- a/drivers/firmware/qcom/Kconfig
>>>> +++ b/drivers/firmware/qcom/Kconfig
>>>> @@ -6,6 +6,14 @@
>>>>  
>>>>  menu "Qualcomm firmware drivers"
>>>>  
>>>> +config QCOM_PAS
>>>> +	tristate
>>>> +	help
>>>> +	  Enable the generic Peripheral Authentication Service (PAS) provided
>>>> +	  by the firmware. It acts as the common layer with different TZ
>>>> +	  backends plugged in whether it's an SCM implementation or a proper
>>>> +	  TEE bus based PAS service implementation.
>>>> +
>>>>  config QCOM_SCM
>>>>  	select QCOM_TZMEM
>>>>  	tristate
>>>> diff --git a/drivers/firmware/qcom/Makefile b/drivers/firmware/qcom/Makefile
>>>> index 0be40a1abc13..dc5ab45f906a 100644
>>>> --- a/drivers/firmware/qcom/Makefile
>>>> +++ b/drivers/firmware/qcom/Makefile
>>>> @@ -8,3 +8,4 @@ qcom-scm-objs += qcom_scm.o qcom_scm-smc.o qcom_scm-legacy.o
>>>>  obj-$(CONFIG_QCOM_TZMEM)	+= qcom_tzmem.o
>>>>  obj-$(CONFIG_QCOM_QSEECOM)	+= qcom_qseecom.o
>>>>  obj-$(CONFIG_QCOM_QSEECOM_UEFISECAPP) += qcom_qseecom_uefisecapp.o
>>>> +obj-$(CONFIG_QCOM_PAS)		+= qcom_pas.o
>>>> diff --git a/drivers/firmware/qcom/qcom_pas.c b/drivers/firmware/qcom/qcom_pas.c
>>>> new file mode 100644
>>>> index 000000000000..beb1bae55546
>>>> --- /dev/null
>>>> +++ b/drivers/firmware/qcom/qcom_pas.c
>>>> @@ -0,0 +1,298 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/*
>>>> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
>>>> + */
>>>> +
>>>> +#include <linux/device/devres.h>
>>>> +#include <linux/firmware/qcom/qcom_pas.h>
>>>> +#include <linux/kernel.h>
>>>> +#include <linux/module.h>
>>>> +
>>>> +#include "qcom_pas.h"
>>>> +
>>>> +struct qcom_pas_ops *ops_ptr;
>>>
>>> Same comment as before. Don't create singletons. And for sure not global
>>> ones.
>>
>> This pattern has been carried from the PAS API contract among kernel
>> clients and the SCM PAS service earlier. The clients don't hold a
>> reference to the PAS data like underlying platform or TEE device etc.
>> Hence the need to have a global data pointer to hold reference to the
>> ops data structure registered by drivers having different lifetime of
>> devices. Also, the PAS APIs can be called from very different client
>> driver contexts.
>>
>> Surely, avoiding global data is always better given a better alternative
>> is there. Do you have any better alternative proposal here?
> 
> Why it cannot be part of the context?
> 
> Look at your API, e.g.:
> qcom_pas_init_image(). It takes struct qcom_pas_context which should
> contain the ops.

This would make the client have to select the ops. The whole point is to
avoid that, since the client has no clue (and is supposed not to have any).

What Sumit does is to bind the ops based on the runtime-discovered
mechanism (which needs to only happen once, given we're not replacing the
TZ at runtime)

Konrad