linux-kernel - Re: [PATCH v2 0/5] imx8mp: add support for the IMX AIPSTZ bridge

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Message-ID: <20250226212219.lthoofw7nrs3gtg6@pengutronix.de>
Date: Wed, 26 Feb 2025 22:22:19 +0100
From: Marco Felsch <m.felsch@...gutronix.de>
To: Laurentiu Mihalcea <laurentiumihalcea111@...il.com>
Cc: 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>,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/5] imx8mp: add support for the IMX AIPSTZ bridge

Hi,

On 25-02-26, 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).

My question still stands:

Setting these bits requires very often that the core is running at EL3
(e.g. secure-monitor) which is not the case for Linux. Can you please
provide more information how Linux can set these bits?

Regards,
  Marco

> The child-parent relationship between the bridge and its peripherals
> should guarantee that the bridge is configured before the AP attempts
> to access the IPs.
> 
> Other masters should use the 'access-controllers' property to enforce
> a dependency between their device and the bridge device (see the DSP,
> for example).
> 
> At the moment, we only want to apply a default, more relaxed
> configuration, which is why the number of access controller cells
> is 0.
> 
> The initial version of the series can be found at [1]. The new version
> should provide better management of the device dependencies.
> 
> [1]: https://lore.kernel.org/linux-arm-kernel/20241119130726.2761726-1-daniel.baluta@nxp.com/
> 
> ---
> Changes in v2:
> * adress Frank Li's comments
> * pick up some A-b/R-b's
> * don't use "simple-bus" as the second compatible. As per Krzysztof's
> comment, AIPSTZ is not a "simple-bus".
> ---
> 
> Laurentiu Mihalcea (5):
>   dt-bindings: bus: add documentation for the IMX AIPSTZ bridge
>   dt-bindings: dsp: fsl,dsp: document 'access-controllers' property
>   bus: add driver for IMX AIPSTZ bridge
>   arm64: dts: imx8mp: convert 'aips5' to 'aipstz5'
>   arm64: dts: imx8mp: make 'dsp' node depend on 'aips5'
> 
>  .../bindings/bus/fsl,imx8mp-aipstz.yaml       | 86 +++++++++++++++++
>  .../devicetree/bindings/dsp/fsl,dsp.yaml      |  3 +
>  arch/arm64/boot/dts/freescale/imx8mp.dtsi     |  9 +-
>  drivers/bus/Kconfig                           |  6 ++
>  drivers/bus/Makefile                          |  1 +
>  drivers/bus/imx-aipstz.c                      | 92 +++++++++++++++++++
>  6 files changed, 194 insertions(+), 3 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/bus/fsl,imx8mp-aipstz.yaml
>  create mode 100644 drivers/bus/imx-aipstz.c
> 
> -- 
> 2.34.1
> 
> 
>