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From:   Benjamin Gaignard <benjamin.gaignard@linaro.org>
Date:   Tue, 27 Feb 2018 20:16:59 +0100
Message-ID: <CA+M3ks6qV_pGdE6mr3n7TiY9VhbqEkrdH6tN=8e-A=oa4UbDHw@mail.gmail.com>
Subject: Re: [PATCH 0/3] STM32 Extended TrustZone Protection driver
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.org>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        devicetree@vger.kernel.org,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Benjamin Gaignard <benjamin.gaignard@st.com>
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2018-02-27 18:11 GMT+01:00 Mark Rutland <mark.rutland@arm.com>:
> On Tue, Feb 27, 2018 at 03:09:23PM +0100, Benjamin Gaignard wrote:
>> On early boot stages STM32MP1 platform is able to dedicate some hardware blocks
>> to a secure OS running in TrustZone.
>> We need to avoid using those hardware blocks on non-secure context (i.e. kernel)
>> because read/write access will all be discarded.
>>
>> Extended TrustZone Protection driver register itself as listener of
>> BUS_NOTIFY_BIND_DRIVER and check, given the device address, if the hardware block
>> could be used in a Linux context. If not it returns NOTIFY_BAD to driver core
>> to stop driver probing.
>
> Huh?
>
> If these devices are not usable from the non-secure side, why are they
> not removed form the DT (or marked disabled)?
>
> In other cases, where resources are carved out for the secure side (e.g.
> DRAM carveouts), that's how we handle things.
>

That true you can parse and disable a device a boot time but if DT doesn't
exactly reflect etzpc status bits we will in trouble when try to get access to
the device.
Changing the DT is a software protection while etzpc is an hardware protection
so we need to check it anyway.

Benjamin


> Mark.
>
>>
>> NOTE: patches 2 and 3 should be applied only on
>> git://git.kernel.org/pub/scm/linux/kernel/git/atorgue/stm32.git stm32-next
>> but until this patch: https://lkml.org/lkml/2018/2/26/386
>> find it way to mailine KBuild will complain about them.
>>
>> Benjamin Gaignard (3):
>>   driver core: check notifier_call_chain return value
>>   dt-bindings: stm32: Add bindings for Extended TrustZone Protection
>>   ARM: mach-stm32: Add Extended TrustZone Protection driver
>>
>>  .../bindings/arm/stm32/st,stm32mp1-etzpc.txt       |  13 ++
>>  arch/arm/mach-stm32/Kconfig                        |   7 +
>>  arch/arm/mach-stm32/Makefile                       |   1 +
>>  arch/arm/mach-stm32/stm32-etzpc.c                  | 252 +++++++++++++++++++++
>>  drivers/base/dd.c                                  |   9 +-
>>  5 files changed, 279 insertions(+), 3 deletions(-)
>>  create mode 100644 Documentation/devicetree/bindings/arm/stm32/st,stm32mp1-etzpc.txt
>>  create mode 100644 arch/arm/mach-stm32/stm32-etzpc.c
>>
>> --
>> 2.15.0
>>