linux-kernel - Re: [PATCH v7 0/7] i2c-atr and FPDLink

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Date:   Fri, 20 Jan 2023 17:17:18 +0100
From:   Luca Ceresoli <luca.ceresoli@...tlin.com>
To:     Andy Shevchenko <andriy.shevchenko@...el.com>
Cc:     Tomi Valkeinen <tomi.valkeinen@...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>,
        Matti Vaittinen <Matti.Vaittinen@...rohmeurope.com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.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>,
        Shawn Tu <shawnx.tu@...el.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Mike Pagano <mpagano@...too.org>,
        Krzysztof Hałasa <khalasa@...p.pl>,
        Marek Vasut <marex@...x.de>
Subject: Re: [PATCH v7 0/7] i2c-atr and FPDLink

Hi Andy,

On Fri, 20 Jan 2023 18:00:02 +0200
Andy Shevchenko <andriy.shevchenko@...el.com> wrote:

> On Thu, Jan 19, 2023 at 09:43:58AM +0100, Luca Ceresoli wrote:
> > On Wed, 18 Jan 2023 19:43:23 +0200
> > Andy Shevchenko <andriy.shevchenko@...el.com> wrote:  
> > > On Wed, Jan 18, 2023 at 07:28:20PM +0200, Tomi Valkeinen wrote:  
> > > > On 18/01/2023 18:01, Andy Shevchenko wrote:    
> > > > > On Wed, Jan 18, 2023 at 02:40:24PM +0200, Tomi Valkeinen wrote:    
> 
> ...
> 
> > > > Can you clarify what you mean here?
> > > > 
> > > > The i2c_clients are not aware of the i2c-atr. They are normal i2c clients.
> > > > The FPD-Link drivers are aware of the ATR, as the FPD-Link hardware contains
> > > > the ATR support.    
> > > 
> > > Can't that hardware be represented as I2C adapter? In such case the ATR specifics
> > > can be hidden from the client (drivers).
> > > 
> > > I'm worrying about code duplication and other things that leak into drivers as
> > > ATR callbacks.  
> > 
> > Which callbacks do you refer to? i2c_atr_ops? I don't think we can do
> > without the attach/detach_client ones, it's where the driver-specific
> > implementation is hooked for the generic ATR infra to call it.
> > 
> > However now I noticed the select/deselect ops are still there. IIRC
> > they are not used by any driver and in the past the plan was to just
> > remove them. Tomi, do you think there is a good reason to keep them?
> >   
> > > It might be that I didn't get how hw exactly functioning on this
> > > level and why we need those callbacks.  
> > 
> > As far as "how hw exactly works", in case you haven't seen that, the
> > best explanation I was able to give is in my ELCE 2019 talk, at minute
> > ~22. It's a 2-3 minute watch. The slides have pointers to other talks
> > and discussion.  
> 
> Probably I have missed the URL in the discussion, care to resend?

I hadn't sent any URL :)

Here's the shortcut to go straight to the ATR description:
https://youtu.be/7hLv6fYAW-E?t=1350

Slides:
https://elinux.org/images/f/fc/Ceresoli-elce2019-video-serdes-linux.pdf

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com