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

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Message-ID: <20201102092110.ro6a456lvbrktwoz@gilmour.lan>
Date:   Mon, 2 Nov 2020 10:21:10 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Helen Koike <helen.koike@...labora.com>
Cc:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-sunxi@...glegroups.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Yong Deng <yong.deng@...ewell.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Hans Verkuil <hverkuil@...all.nl>, kevin.lhopital@...mail.com
Subject: Re: [PATCH 08/14] media: sunxi: Add support for the A31 MIPI CSI-2
 controller

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

Maxime

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