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Date:   Thu, 19 Jan 2023 09:43:58 +0100
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 =?UTF-8?Q?Ha=C5=82asa?= <khalasa@piap.pl>,
        Marek Vasut <marex@denx.de>
Subject: Re: [PATCH v7 0/7] i2c-atr and FPDLink
Message-ID: <20230119094358.010bc826@booty>
In-Reply-To: <Y8gvu/E5EoPqo8J1@smile.fi.intel.com>
References: <20230118124031.788940-1-tomi.valkeinen@ideasonboard.com>
        <Y8gX0krXayfOa4Hi@smile.fi.intel.com>
        <bd6d6cc0-4e70-fa31-4b5e-e6bcddf62d36@ideasonboard.com>
        <Y8gvu/E5EoPqo8J1@smile.fi.intel.com>
Organization: Bootlin
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Hi Andy,

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:  
> > > > Hi,
> > > > 
> > > > You can find the v6 from:
> > > > 
> > > > https://lore.kernel.org/all/20230105140307.272052-1-tomi.valkeinen@ideasonboard.com/
> > > > 
> > > > Main changes:
> > > > 
> > > > * i2c-atr: Use bus notifier. This allows us to drop the patch that adds
> > > >    the attach_client/detach_client callbacks. On the downside, it removes
> > > >    the option for error handling if the translation setup fails, and also
> > > >    doesn't provide us the pointer to the i2c_board_info. I belive both
> > > >    are acceptable downsides.
> > > > 
> > > > * Use fwnode in the fpdlink drivers instead of OF
> > > > 
> > > > * Addressed all the review comments (I hope)
> > > > 
> > > > * Lots of cosmetic or minor fixes which I came up while doing the fwnode
> > > >    change  
> > > 
> > > I believe my comments to the first driver applies to the next two, so please
> > > address them whenever you are agree / it's possible / it makes sense.
> > > 
> > > About ATR implementation. We have the i2c bus (Linux representation of
> > > the driver model) and i2c_adapter and i2c_client objects there. Can't we
> > > have an i2c_client_aliased in similar way and be transparent with users?  
> 
> > 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.

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