linux-kernel - Re: [PATCH] tee: optee: Populate child nodes in probe function

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Date:   Thu, 10 Nov 2022 12:09:53 +0000
From:   Ludvig Pärsson <Ludvig.Parsson@...s.com>
To:     "sumit.garg@...aro.org" <sumit.garg@...aro.org>,
        Ludvig Pärsson <Ludvig.Parsson@...s.com>
CC:     "jens.wiklander@...aro.org" <jens.wiklander@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kernel <kernel@...s.com>,
        "op-tee@...ts.trustedfirmware.org" <op-tee@...ts.trustedfirmware.org>
Subject: Re: [PATCH] tee: optee: Populate child nodes in probe function

On Thu, 2022-11-10 at 16:23 +0530, Sumit Garg wrote:
> On Wed, 9 Nov 2022 at 21:37, Ludvig Pärsson <ludvig.parsson@...s.com>
> wrote:
> > 
> > Currently there is no dependency between the "linaro,scmi-optee"
> > driver
> > and the tee_core. If the scmi-optee driver gets probed before the
> > tee_bus_type is initialized, then we will get an unwanted error
> > print.
> > 
> 
> What error print do you observe? I suppose this case is already
> handled by scmi optee driver via -EPROBE_DEFER.
> 
> -Sumit
> 
Hi Sumit,

The error print is in driver_register().

This is kind of what happens:
scmi_driver_init()
scmi_probe()
    scmi_optee_link_supplier()
        scmi_optee_init()
            driver_register() <--- pr_err() if tee_bus_type is not
initialized
tee_init() <--- tee_bus_type gets initialized here

The scmi_optee_link_supplier() will always return -EPROBE_DEFER the
first time because scmi_optee_private is initialized in
scmi_optee_service_probe, which is only called after the driver is
registered in scmi_optee_init. Right now the driver_register fails
because tee_bus_type is not initialized which is printing the unwanted
error print. Another side effect of this is that
scmi_optee_link_supplier() will return -EPROBE_DEFER a second time, and
scmi_probe will be successful the third time instead of the second
time.

BR,
Ludvig

> > This patch enables putting scmi-optee nodes as children to the
> > optee
> > node in devicetree, which indirectly creates the missing
> > dependency.
> > 
> > Signed-off-by: Ludvig Pärsson <ludvig.parsson@...s.com>
> > ---
> >  drivers/tee/optee/smc_abi.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/tee/optee/smc_abi.c
> > b/drivers/tee/optee/smc_abi.c
> > index a1c1fa1a9c28..be6f02fd5a7f 100644
> > --- a/drivers/tee/optee/smc_abi.c
> > +++ b/drivers/tee/optee/smc_abi.c
> > @@ -1533,6 +1533,11 @@ static int optee_probe(struct
> > platform_device *pdev)
> >         if (rc)
> >                 goto err_disable_shm_cache;
> > 
> > +       /* Populate any dependent child node (if any) */
> > +       rc = devm_of_platform_populate(&pdev->dev);
> > +       if (rc)
> > +               goto err_disable_shm_cache;
> > +
> >         pr_info("initialized driver\n");
> >         return 0;
> > 
> > --
> > 2.30.2
> >