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

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Message-ID: <515a21fa-17f4-1f73-ed5c-adcc7f74ddb3@ideasonboard.com>
Date:   Fri, 20 Jan 2023 18:20:53 +0200
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Luca Ceresoli <luca.ceresoli@...tlin.com>,
        Andy Shevchenko <andriy.shevchenko@...el.com>
Cc:     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

On 20/01/2023 18:17, Luca Ceresoli wrote:
> 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

A small note: the current implementation doesn't match the slides, as 
the adapter is now (at least kind of) in the serializer (the "ideal 
solution" in the slides.

  Tomi