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

From: Luca Ceresoli <luca.ceresoli@bootlin.com>
To: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: "Tomi Valkeinen" <tomi.valkeinen@ideasonboard.com>,
	linux-media@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org,
	"Rob Herring" <robh+dt@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Wolfram Sang" <wsa@kernel.org>,
	"Matti Vaittinen" <Matti.Vaittinen@fi.rohmeurope.com>,
	"Laurent Pinchart" <laurent.pinchart+renesas@ideasonboard.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Peter Rosin" <peda@axentia.se>,
	"Liam Girdwood" <lgirdwood@gmail.com>,
	"Mark Brown" <broonie@kernel.org>,
	"Sakari Ailus" <sakari.ailus@linux.intel.com>,
	"Michael Tretter" <m.tretter@pengutronix.de>,
	"Shawn Tu" <shawnx.tu@intel.com>,
	"Hans Verkuil" <hverkuil@xs4all.nl>,
	"Mike Pagano" <mpagano@gentoo.org>,
	"Krzysztof Hałasa" <khalasa@piap.pl>,
	"Marek Vasut" <marex@denx.de>
Subject: Re: [PATCH v7 0/7] i2c-atr and FPDLink
Date: Fri, 20 Jan 2023 17:17:18 +0100	[thread overview]
Message-ID: <20230120171718.3674af61@booty> (raw)
In-Reply-To: <Y8q6ggmOsygyVdTT@smile.fi.intel.com>

Hi Andy,

On Fri, 20 Jan 2023 18:00:02 +0200
Andy Shevchenko <andriy.shevchenko@intel.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@intel.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