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

From: Benjamin Gaignard <benjamin.gaignard@collabora.com>
To: Philipp Zabel <p.zabel@pengutronix.de>,
	robh+dt@kernel.org, shawnguo@kernel.org, s.hauer@pengutronix.de,
	festevam@gmail.com, ezequiel@collabora.com, mchehab@kernel.org,
	gregkh@linuxfoundation.org
Cc: kernel@pengutronix.de, linux-imx@nxp.com,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
	linux-rockchip@lists.infradead.org, devel@driverdev.osuosl.org,
	kernel@collabora.com
Subject: Re: [PATCH v3 0/5] Reset driver for IMX8MQ VPU hardware block
Date: Wed, 3 Mar 2021 16:20:34 +0100	[thread overview]
Message-ID: <2d55ad69-9b93-ab0e-04af-cd775cc9248b@collabora.com> (raw)
In-Reply-To: <e6f8537d2a1f34d0a424b68e056c0ae556c93efd.camel@pengutronix.de>

Le 03/03/2021 à 15:17, Philipp Zabel a écrit :
> 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.

They are all part of the control block and of the reset process for this
hardware that why I put them here. I guess it is border line :-)

>
>> 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.

I will give a try in this direction.

>
>> 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.

If I want to use a syscon (or a reset) the driver must not ioremap the "ctrl"
registers. It means that "ctrl" has to be removed from the driver requested
reg-names (imx8mq_reg_names[]). Doing that break the kernel/DT compatibility.
Somehow syscon and "ctrl" are exclusive.

Benjamin

>
> regards
> Philipp
>