Date:   Fri, 27 Jan 2023 11:15:01 +0200
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Wolfram Sang <wsa@...nel.org>,
        Luca Ceresoli <luca.ceresoli@...tlin.com>,
        Matti Vaittinen <Matti.Vaittinen@...rohmeurope.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Peter Rosin <peda@...ntia.se>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Michael Tretter <m.tretter@...gutronix.de>,
        Hans Verkuil <hverkuil@...all.nl>,
        Mike Pagano <mpagano@...too.org>,
        Krzysztof Hałasa <khalasa@...p.pl>,
        Marek Vasut <marex@...x.de>
Subject: Re: [PATCH v7 5/7] media: i2c: add DS90UB960 driver

On Fri, Jan 27, 2023 at 10:24:04AM +0200, Tomi Valkeinen wrote:
> On 26/01/2023 12:51, Laurent Pinchart wrote:
> > On Thu, Jan 26, 2023 at 12:21:06PM +0200, Andy Shevchenko wrote:
> > > On Thu, Jan 26, 2023 at 10:41:47AM +0200, Tomi Valkeinen wrote:
> > > > On 25/01/2023 17:27, Andy Shevchenko wrote:

...

> > > > > But I probably don't understand the ATR structure and what exactly we need to
> > > > > pass to it, perhaps it also can be replaced with properties (note, that we have
> > > > > some interesting ones that called references, which is an alternative to DT
> > > > > phandle).
> > > > 
> > > > Well, maybe this needs a Linux bus implementation. I'm not that familiar
> > > > with implementing a bus, but I think that would make it easier to share data
> > > > between the deserializer and the serializer. A bus sounds a bit like an
> > > > overkill for a 1-to-1 connection, used by a few drivers, but maybe it
> > > > wouldn't be too much code.
> > > 
> > > Have you looked at auxiliary bus (appeared a few releases ago in kernel)?
> > 
> > As far as I understand, the auxiliary bus infrastructure is meant for
> > use cases where a single hardware device needs to be split into multiple
> > logical devices (as in struct device). Platform devices were
> > historically (ab)used for this, and the auxiliary bus is meant as a
> > cleaner solution. I'm not sure if it would be a good match here, or if
> > it would be considered an abuse of the auxiliary bus API.
> 
> The aux bus docs say "A key requirement for utilizing the auxiliary bus is
> that there is no dependency on a physical bus, device, register accesses or
> regmap support. These individual devices split from the core cannot live on
> the platform bus as they are not physical devices that are controlled by
> DT/ACPI.", which doesn't sound like a good fit.

Thanks for checking!

> The deserializer and serializers are currently independent devices and
> drivers (the pdata is the only shared thing), but I think we may need
> something better here. The devices are more tightly tied together than
> "normal" video devices, in my opinion, as the serializer is fully controlled
> by the deserializer (including power).
> 
> And if we ever want to implement something like power management, we
> probably need something more than what we have now. Although I don't know
> how that would be done, as all the peripherals behind the serializer would
> also lose power...

I believe you have to create a power domain for them and when such device
is added, the power domain of it should belong to the serialized.

-- 
With Best Regards,
Andy Shevchenko

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