Re: [PATCH 08/14] media: sunxi: Add support for the A31 MIPI CSI-2 controller

From: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
To: Maxime Ripard <maxime@cerno.tech>
Cc: Helen Koike <helen.koike@collabora.com>,
	linux-media@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org,
	linux-sunxi@googlegroups.com,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Rob Herring <robh+dt@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
	Yong Deng <yong.deng@magewell.com>,
	Kishon Vijay Abraham I <kishon@ti.com>,
	Vinod Koul <vkoul@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Philipp Zabel <p.zabel@pengutronix.de>,
	Hans Verkuil <hans.verkuil@cisco.com>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Hans Verkuil <hverkuil@xs4all.nl>,
	kevin.lhopital@hotmail.com
Subject: Re: [PATCH 08/14] media: sunxi: Add support for the A31 MIPI CSI-2 controller
Date: Wed, 4 Nov 2020 12:17:10 +0100	[thread overview]
Message-ID: <20201104111710.GB287014@aptenodytes> (raw)
In-Reply-To: <20201102092110.ro6a456lvbrktwoz@gilmour.lan>

[-- Attachment #1: Type: text/plain, Size: 2132 bytes --]

Hi,

On Mon 02 Nov 20, 10:21, Maxime Ripard wrote:
> On Fri, Oct 30, 2020 at 07:45:18PM -0300, Helen Koike wrote:
> > On 10/23/20 2:45 PM, Paul Kocialkowski wrote:
> > > The A31 MIPI CSI-2 controller is a dedicated MIPI CSI-2 controller
> > > found on Allwinner SoCs such as the A31 and V3/V3s.
> > > 
> > > It is a standalone block, connected to the CSI controller on one side
> > > and to the MIPI D-PHY block on the other. It has a dedicated address
> > > space, interrupt line and clock.
> > > 
> > > Currently, the MIPI CSI-2 controller is hard-tied to a specific CSI
> > > controller (CSI0) but newer SoCs (such as the V5) may allow switching
> > > MIPI CSI-2 controllers between CSI controllers.
> > > 
> > > It is represented as a V4L2 subdev to the CSI controller and takes a
> > > MIPI CSI-2 sensor as its own subdev, all using the fwnode graph and
> > > media controller API.
> > 
> > Maybe this is a bad idea, but I was thinking:
> > This driver basically just turn on/off and catch some interrupts for errors,
> > and all the rest of v4l2 config you just forward to the next subdevice
> > on the pipeline.
> > 
> > So instead of exposing it as a subdevice, I was wondering if modeling
> > this driver also through the phy subsystem wouldn't be cleaner, so
> > you won't need all the v4l2 subdevice/topology boilerplate code that
> > it seems you are not using (unless you have plans to add controls or
> > some specific configuration on this node later).
> > 
> > But this would require changes on the sun6i-csi driver.
> > 
> > What do you think?
> 
> Eventually we'll need to filter the virtual channels / datatypes I
> guess, so it's definitely valuable to have it in v4l2

Agreed and like I mentionned in the discussion on 00/14 I don't think it
would be a cleaner way to expose things.

There's also the fact that newer SoCs like the V5 seem to allow connecting
any MIPI CSI-2 controller to any CSI controller, so the graph representation
is definitely welcome here.

Paul

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]