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From: Philipp Zabel <p.zabel@pengutronix.de>
To: Benjamin Gaignard <benjamin.gaignard@collabora.com>,
	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, 03 Mar 2021 17:25:18 +0100	[thread overview]
Message-ID: <c12d84b955b0265dbcf89f2d7fc4d5c28bc74756.camel@pengutronix.de> (raw)
In-Reply-To: <2d55ad69-9b93-ab0e-04af-cd775cc9248b@collabora.com>

On Wed, 2021-03-03 at 16:20 +0100, Benjamin Gaignard wrote:
> 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 :-)

I'm pushing back to keep the reset control framework focused on
controlling reset lines. Every side effect (such as the asymmetric clock
ungating) in a random driver makes it harder to reason about behaviour
at the API level, and to review patches for hardware I am not familiar
with.

> > > 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.

Thank you.

> > > 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.

The way the driver is set up currently, yes. You could add a bit of
platform specific probe code, though, that would set up the regmap
either by calling
	syscon_regmap_lookup_by_phandle();
for the new binding, or, if the phandle is not available, fall back to
	platform_get_resource_byname(..., "ctrl");
	devm_ioremap_resource();
	devm_regmap_init_mmio();
for the old binding.
The actual codec .reset and variant .runtime_resume ops could be
identical then.

regards
Philipp

  reply	other threads:[~2021-03-03 19:09 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-01 15:17 [PATCH v3 0/5] Reset driver for IMX8MQ VPU hardware block Benjamin Gaignard
2021-03-01 15:17 ` [PATCH v3 1/5] dt-bindings: reset: IMX8MQ VPU reset Benjamin Gaignard
2021-03-08 18:23   ` Rob Herring
2021-03-01 15:17 ` [PATCH v3 2/5] dt-bindings: media: IMX8MQ VPU: document reset usage Benjamin Gaignard
2021-03-08 18:27   ` Rob Herring
2021-03-01 15:17 ` [PATCH v3 3/5] reset: Add reset driver for IMX8MQ VPU block Benjamin Gaignard
2021-03-03 14:33   ` Philipp Zabel
2021-03-01 15:17 ` [PATCH v3 4/5] media: hantro: Use reset driver Benjamin Gaignard
2021-03-03 14:39   ` Philipp Zabel
2021-03-03 14:48     ` Benjamin Gaignard
2021-03-01 15:17 ` [PATCH v3 5/5] arm64: dts: imx8mq: Use reset driver for VPU hardware block Benjamin Gaignard
2021-03-03 14:17 ` [PATCH v3 0/5] Reset driver for IMX8MQ " Philipp Zabel
2021-03-03 15:20   ` Benjamin Gaignard
2021-03-03 16:25     ` Philipp Zabel [this message]
2021-03-04 12:52       ` Adam Ford
2021-03-05  9:35       ` Benjamin Gaignard
2021-03-08 18:22 ` Rob Herring
2021-03-08 18:26   ` Rob Herring

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