linux-kernel - Re: [PATCH 2/2] arm64: dts: imx8mm: Add Crypto CAAM support

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Message-ID: <fd146818-98c9-7092-5d49-a985db5900c7@kontron.de>
Date:   Wed, 11 Dec 2019 14:36:24 +0000
From:   Schrempf Frieder <frieder.schrempf@...tron.de>
To:     Adam Ford <aford173@...il.com>, Horia Geanta <horia.geanta@....com>
CC:     Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Aymen Sghaier <aymen.sghaier@....com>,
        "Herbert Xu" <herbert@...dor.apana.org.au>,
        Fabio Estevam <festevam@...il.com>,
        "Sascha Hauer" <s.hauer@...gutronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "Pengutronix Kernel Team" <kernel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH 2/2] arm64: dts: imx8mm: Add Crypto CAAM support

Hi Adam,

On 09.12.19 17:47, Adam Ford wrote:
> On Mon, Dec 9, 2019 at 10:23 AM Horia Geanta <horia.geanta@....com> wrote:
>>
>> On 12/1/2019 12:52 AM, Adam Ford wrote:
>>> The i.MX8M Mini supports the same crypto engine as what is in
>>> the i.MX8MQ, but it is not currently present in the device tree,
>>> because it may be resricted by security features.
>>>
>> What exactly are you referring to?
> 
> I don't know this hardware very well, but on a different platform, we
> needed to make the crypto engines as disabled if they were being
> accessed through secure operations which made it unavailable to Linux
> without using some special barriers. I didn't have the special
> hardware on the other platform that required it that way, so I can't
> really explain it well.  I know on those special cases, because some
> people were accessing these registers through other means, the devices
> had to be marked as 'disabled' so to avoid breaking something.  Since
> I wasn't sure if this was left out of the i.MX8M Mini on purpose, I
> let this disabled just in case this hardware platform was also
> affected in a similar and people wanting to use it could mark it as
> 'okay'

I don't know enough about this to understand the problem you're 
describing. It seems like most SoCs have the CAAM enabled by default in 
the devicetree. On first glance I could only find fsl-lx2160a.dtsi that 
has it disabled.

> 
> adam
> 
>>
>>> This patch places in into the device tree and marks it as disabled,
>>> but anyone not restricting the CAAM with secure mode functions
>>> can mark it as enabled.
>>>
>> Even if - due to export control regulations - CAAM is "trimmed down",
>> it loses only the encryption capabilities (hashing etc. still working).

I don't know much about this, but as Horia said the CAAM might have 
limited capabilities in some cases but would still work.

Therefore I think the CAAM should be enabled by default as it already is 
done for most other SoCs.

Regards,
Frieder

>>
>> Again, please clarify what you mean by "secure mode functions",
>> "security features" etc.
>>
>> Horia
> 
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> 

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