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

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Date:   Mon, 9 Dec 2019 10:47:14 -0600
From:   Adam Ford <aford173@...il.com>
To:     Horia Geanta <horia.geanta@....com>
Cc:     "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        Aymen Sghaier <aymen.sghaier@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] arm64: dts: imx8mm: Add Crypto CAAM support

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'

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