linux-kernel - Re: [PATCH RFC 1/3] firmware: qcom: implement object invoke support

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Message-ID: <gtdr5s7yih7pjuhpfkjmlu2lflya4heiph4wi446rlbxduqlya@5xfix7dyocli>
Date: Thu, 25 Jul 2024 07:09:30 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Amirreza Zarrabi <quic_azarrabi@...cinc.com>
Cc: Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, Sumit Semwal <sumit.semwal@...aro.org>, 
	Christian König <christian.koenig@....com>, srinivas.kandagatla@...aro.org, bartosz.golaszewski@...aro.org, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH RFC 1/3] firmware: qcom: implement object invoke support

On Thu, Jul 25, 2024 at 01:19:07PM GMT, Amirreza Zarrabi wrote:
> 
> 
> On 7/4/2024 5:34 PM, Dmitry Baryshkov wrote:
> > On Thu, 4 Jul 2024 at 00:40, Amirreza Zarrabi <quic_azarrabi@...cinc.com> wrote:
> >>
> >>
> >>
> >> On 7/3/2024 10:13 PM, Dmitry Baryshkov wrote:
> >>> On Tue, Jul 02, 2024 at 10:57:36PM GMT, Amirreza Zarrabi wrote:
> >>>> Qualcomm TEE hosts Trusted Applications and Services that run in the
> >>>> secure world. Access to these resources is provided using object
> >>>> capabilities. A TEE client with access to the capability can invoke
> >>>> the object and request a service. Similarly, TEE can request a service
> >>>> from nonsecure world with object capabilities that are exported to secure
> >>>> world.
> >>>>
> >>>> We provide qcom_tee_object which represents an object in both secure
> >>>> and nonsecure world. TEE clients can invoke an instance of qcom_tee_object
> >>>> to access TEE. TEE can issue a callback request to nonsecure world
> >>>> by invoking an instance of qcom_tee_object in nonsecure world.
> >>>
> >>> Please see Documentation/process/submitting-patches.rst on how to write
> >>> commit messages.
> >>
> >> Ack.
> >>
> >>>
> >>>>
> >>>> Any driver in nonsecure world that is interested to export a struct (or a
> >>>> service object) to TEE, requires to embed an instance of qcom_tee_object in
> >>>> the relevant struct and implements the dispatcher function which is called
> >>>> when TEE invoked the service object.
> >>>>
> >>>> We also provids simplified API which implements the Qualcomm TEE transport
> >>>> protocol. The implementation is independent from any services that may
> >>>> reside in nonsecure world.
> >>>
> >>> "also" usually means that it should go to a separate commit.
> >>
> >> I will split this patch to multiple smaller ones.
> >>
> > 
> > [...]
> > 
> >>>
> >>>> +    } in, out;
> >>>> +};
> >>>> +
> >>>> +int qcom_tee_object_do_invoke(struct qcom_tee_object_invoke_ctx *oic,
> >>>> +    struct qcom_tee_object *object, unsigned long op, struct qcom_tee_arg u[], int *result);
> >>>
> >>> What's the difference between a result that gets returned by the
> >>> function and the result that gets retuned via the pointer?
> >>
> >> The function result, is local to kernel, for instance memory allocation failure,
> >> or failure to issue the smc call. The result in pointer, is the remote result,
> >> for instance return value from TA, or the TEE itself.
> >>
> >> I'll use better name, e.g. 'remote_result'?
> > 
> > See how this is handled by other parties. For example, PSCI. If you
> > have a standard set of return codes, translate them to -ESOMETHING in
> > your framework and let everybody else see only the standard errors.
> > 
> > 
> 
> I can not hide this return value, they are TA dependent. The client to a TA
> needs to see it, just knowing that something has failed is not enough in
> case they need to do something based on that. I can not even translate them
> as they are TA related so the range is unknown.

I'd say it a sad design. At least error values should be standard.

-- 
With best wishes
Dmitry