linux-kernel - Re: [PATCH v7 0/6] imx8mp: add support for the IMX AIPSTZ bridge

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Message-ID: <10ef8a9a-6d23-4fb9-933f-71ab493d21c7@gmail.com>
Date: Thu, 3 Jul 2025 11:51:31 +0300
From: Laurentiu Mihalcea <laurentiumihalcea111@...il.com>
To: Ahmad Fatoum <a.fatoum@...gutronix.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
 Sascha Hauer <s.hauer@...gutronix.de>, Fabio Estevam <festevam@...il.com>,
 Daniel Baluta <daniel.baluta@....com>, Shengjiu Wang
 <shengjiu.wang@....com>, Frank Li <Frank.Li@....com>,
 Marco Felsch <m.felsch@...gutronix.de>,
 Marc Kleine-Budde <mkl@...gutronix.de>,
 Alexander Stein <alexander.stein@...tq-group.com>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org,
 Pengutronix Kernel Team <kernel@...gutronix.de>, imx@...ts.linux.dev
Subject: Re: [PATCH v7 0/6] imx8mp: add support for the IMX AIPSTZ bridge



On 7/3/2025 11:11 AM, Ahmad Fatoum wrote:
> Hello Laurentiu,
>
> On 10.06.25 18:01, Laurentiu Mihalcea wrote:
>> From: Laurentiu Mihalcea <laurentiu.mihalcea@....com>
>>
>> The AIPSTZ bridge offers some security-related configurations which can
>> be used to restrict master access to certain peripherals on the bridge.
>>
>> Normally, this could be done from a secure environment such as ATF before
>> Linux boots but the configuration of AIPSTZ5 is lost each time the power
>> domain is powered off and then powered on. Because of this, it has to be
>> configured each time the power domain is turned on and before any master
>> tries to access the peripherals (e.g: AP, CM7, DSP, on i.MX8MP).
> Sorry if this has been asked before, but I hoped the cover letter or patch
> 3/6 would explain if it were.
>
> What is the default configuration for the AIPSTZ before this series?

the default configuration is the reset configuration since AIPSTZ registers go
back to their reset values during domain power cycling.

> I assume the SAIs under AIPS5 can be accessed by SDMA already, so why was
> changing the AIPSTZ settings needed for the DSP to work?

AFAIK SDMA transactions to peripherals don't go through AIPS5. They use SPBA, which
is why SDMA works even w/o this series. As for the DSP: transactions to peripherals go
through AIPS5. With the reset configuration, the DSP is not allowed to access said peripherals,
which is why this series was needed.