linux-kernel - Re: [PATCH v3 0/5] Reset driver for IMX8MQ VPU hardware block

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Date:   Wed, 03 Mar 2021 15:17:53 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        robh+dt@...nel.org, shawnguo@...nel.org, s.hauer@...gutronix.de,
        festevam@...il.com, ezequiel@...labora.com, mchehab@...nel.org,
        gregkh@...uxfoundation.org
Cc:     kernel@...gutronix.de, linux-imx@....com,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, devel@...verdev.osuosl.org,
        kernel@...labora.com
Subject: Re: [PATCH v3 0/5] Reset driver for IMX8MQ VPU hardware block

Hi Benjamin,

On Mon, 2021-03-01 at 16:17 +0100, Benjamin Gaignard wrote:
> The two VPUs inside IMX8MQ share the same control block which can be see
> as a reset hardware block.

This isn't a reset controller though. The control block also contains
clock gates of some sort and a filter register for the featureset fuses.
Those shouldn't be manipulated via the reset API.

> In order to be able to add the second VPU (for HECV decoding) it will be
> more handy if the both VPU drivers instance don't have to share the
> control block registers. This lead to implement it as an independ reset 
> driver and to change the VPU driver to use it.

Why not switch to a syscon regmap for the control block? That should
also allow to keep backwards compatibility with the old binding with
minimal effort.

> Please note that this series break the compatibility between the DTB and
> kernel. This break is limited to IMX8MQ SoC and is done when the driver
> is still in staging directory.

I know in this case we are pretty sure there are no users of this
binding except for a staging driver, but it would still be nice to keep
support for the deprecated binding, to avoid the requirement of updating
kernel and DT in lock-step.

regards
Philipp