Re: [PATCH v2 2/4] mmc: Mediatek: enable crypto hardware engine

[Linus Walleij <linus.walleij@linaro.org>]

Hi Eric,

thanks for stepping in and clarifying! I get it better now, I though
this was some other encryption scheme "on the side".

There is one worrying thing in the patch still:

On Thu, Mar 11, 2021 at 8:08 PM Eric Biggers <ebiggers@kernel.org> wrote:
> On Thu, Mar 11, 2021 at 02:48:23PM +0100, Linus Walleij wrote:
> > On Tue, Mar 9, 2021 at 3:06 AM Peng Zhou <peng.zhou@mediatek.com> wrote:

> > > +       /*
> > > +        * 1: MSDC_AES_CTL_INIT
> > > +        * 4: cap_id, no-meaning now
> > > +        * 1: cfg_id, we choose the second cfg group
> > > +        */
> > > +       if (mmc->caps2 & MMC_CAP2_CRYPTO)
> > > +               arm_smccc_smc(MTK_SIP_MMC_CONTROL,
> > > +                             1, 4, 1, 0, 0, 0, 0, &smccc_res);

So MSDC_AES_CTL_INIT. Assumes we are using AES and AES
only I suppose?

> It happens in the same place, cqhci-crypto.c.  Mediatek's eMMC inline encryption
> hardware follows the eMMC standard fairly closely, so Peng's patch series just
> sets MMC_CAP2_CRYPTO to make it use the standard cqhci crypto code, and does a
> couple extra things to actually enable the hardware's crypto support on Mediatek
> platforms since it isn't enabled by default.  (*Why* it requires an SMC call to
> enable instead of just working as expected, I don't know though.)

Now I don't know the limitations of cqhci crypto. Clearly it only supports
AES today.

However would the cqhci crypto grow support for any other crypto
like 2Fish or DES and the user request this, then I suppose there is
no way for the MTK driver to announce "uh no I don't do that"?

Or will this cqhci hardware only ever support AES?

Yours,
Linus Walleij