MIME-Version: 1.0
References: <20190222100613.2290-1-christopher.spencer@sea.co.uk>
 <20190222100613.2290-5-christopher.spencer@sea.co.uk> <VI1PR0402MB34851F1E7021F16B45F74E55987A0@VI1PR0402MB3485.eurprd04.prod.outlook.com>
In-Reply-To: <VI1PR0402MB34851F1E7021F16B45F74E55987A0@VI1PR0402MB3485.eurprd04.prod.outlook.com>
From:   Chris Spencer <spencercw@gmail.com>
Date:   Mon, 25 Feb 2019 14:36:43 +0000
Message-ID: <CAGUNXRTvXVU7vRicF=mR7xxCj=p+Sqj3aNnL2TezLZXhHFkvzA@mail.gmail.com>
Subject: Re: [RFC 4/4] crypto: caam - use job ring for RNG instantiation
 instead of DECO
To:     Horia Geanta <horia.geanta@nxp.com>
Cc:     Aymen Sghaier <aymen.sghaier@nxp.com>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        Chris Spencer <christopher.spencer@sea.co.uk>,
        dl-linux-imx <linux-imx@nxp.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-crypto-owner@vger.kernel.org
Precedence: bulk

On Mon, 25 Feb 2019 at 14:22, Horia Geanta <horia.geanta@nxp.com> wrote:
>
> On 2/22/2019 12:07 PM, spencercw@gmail.com wrote:
> > From: Chris Spencer <christopher.spencer@sea.co.uk>
> >
> > This is required to support the i.MX8.
> >
> Why exactly is this required?
> You should provide more details.

I don't know. :) These changes were made in [1], although the change
is actually described in [2] where it says: "Use a Job ring for RNG
instantiation rather than DECO, even for i.MX6/7 families." This does
indeed seem to be necessary to get it to work, but I can only
speculate why.

The original commit which added the run_descriptor_deco0 function [3]
states "[...] and another function that performs the running of the
said descriptor using the DECO debug mechanism." My best guess is that
the DECO debug mechanism is no longer available so it has to go via
the job ring.

> Strictly related to the implementation, why is the code moved to a new file?
> Please do not shuffle the code without providing a good reason.

This was done in an attempt to keep it reasonably close to the changes
in the downstream driver. The file was moved in [1] with the
description "Move the code related to RNG instanciation to another
file to ease comprehension."

The RNG initialisation code is not really needed in ctrl.c anymore
since it is only used in jr.c, so moving it out seems sensible.

Thanks,
Chris

[1] https://source.codeaurora.org/external/imx/linux-imx/commit/drivers/crypto/caam/inst_rng.c?h=imx_4.14.78_1.0.0_ga&id=5fd8fe866172c38e8cd07741d98d79b995f05bc9
[2] https://source.codeaurora.org/external/imx/linux-imx/commit/drivers/crypto/caam/ctrl.c?h=imx_4.14.78_1.0.0_ga&id=afa53c2c96a54b4432a26372e3b5e7dbccbb9671
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/crypto/caam/ctrl.c?id=04cddbfe6b5f334aa337a1a9797eb8914822f2f8