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Date:   Wed, 4 Jan 2023 17:43:45 +0200
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Subject: Re: [PATCH v5 7/8] media: i2c: add DS90UB913 driver
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To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     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>,
        Luca Ceresoli <luca.ceresoli@bootlin.com>,
        Andy Shevchenko <andriy.shevchenko@intel.com>,
        Matti Vaittinen <Matti.Vaittinen@fi.rohmeurope.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>,
        =?UTF-8?Q?Krzysztof_Ha=c5=82asa?= <khalasa@piap.pl>,
        Marek Vasut <marex@denx.de>
References: <20221208104006.316606-1-tomi.valkeinen@ideasonboard.com>
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From:   Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
In-Reply-To: <Y7Wb/Z3627D3HQJb@pendragon.ideasonboard.com>
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On 04/01/2023 17:32, Laurent Pinchart wrote:
> On Wed, Jan 04, 2023 at 04:13:17PM +0200, Tomi Valkeinen wrote:
>> On 04/01/2023 15:55, Laurent Pinchart wrote:
>>> Hi Tomi,
>>>
>>> On Mon, Dec 26, 2022 at 09:25:34PM +0200, Tomi Valkeinen wrote:
>>>> On 26/12/2022 18:56, Laurent Pinchart wrote:
>>>>> On Wed, Dec 14, 2022 at 08:36:47AM +0200, Tomi Valkeinen wrote:
>>>>>> On 14/12/2022 08:29, Tomi Valkeinen wrote:
>>>>>>
>>>>>>>> wondering if the struct device of the DS90UB913 could be passed instead
>>>>>>>> of the port, to avoid passing the port throught
>>>>>>>> ds90ub9xx_platform_data.
>>>>>>>
>>>>>>> Interesting thought. That would limit the number of remote i2c busses to
>>>>>>> one, though. Not a problem for FPD-Link, but I wonder if that's assuming
>>>>>>> too much for the future users. Then again, this is an in-kernel API so
>>>>>>> we could extend it later if needed. So I'll try this out and see if I
>>>>>>> hit any issues.
>>>>>>
>>>>>> Right, so the issue with this one would be that it would prevent a
>>>>>> single device uses. E.g. a single chip which acts as an ATR (similar to
>>>>>> i2c-mux chips), i.e. it contains both the main and the remote i2c busses.
>>>>>
>>>>> I don't think I understand this, sorry.
>>>>
>>>> What you are suggesting above means that we'd have a separate device for
>>>> each port of the ATR. Which is fine in our current case, as the i2c
>>>> master busses are behind separate remote devices.
>>>>
>>>> But if you consider a case similar to i2c-mux, where we have a single
>>>> chip with the slave bus and, say, 4 master busses. We would probably
>>>> have only a single device for that.
>>>
>>> Hmmm... Yes you're right, it won't work in that case. Maybe we could
>>> have two functions, the existing i2c_atr_add_adapter(), and another one
>>> that wraps it ? It would be nice if we could get rid of the platform
>>> data for the UB913 and UB953 drivers.
>>
>> I wouldn't mind that at all, but we already have the bc_rate there. And
>> I have a feeling that we might need more if we implement more features.
> 
> Indeed. I feel that platform data is a bit of a hack here, but maybe
> it's not that bad.
> 
>> And we also have the atr pointer there. Or do you think that could be
>> dropped also? In your mail above you only mention the port, but maybe
>> the deser could register the serializer device and port to the ATR, and
>> then the ser could just use its device pointer instead of atr & port.
> 
> I was wondering if we could drop the atr pointer too, yes. I'm not sure
> how, and there's no urgency to fix this. My main concern is that new
> drivers should ideally not be forced to use platform data just for ATR
> support, if they don't use it already for something else.

Good point. However, we don't know who will use ATR or how ATR is going 
to be used. Using it the same way i2c-mux is used, there's no problem 
and platform data is not needed. Using it in this split manner we do 
with FPDLink does bring up the problem. And using i2c-mux in the split 
manner would also bring up the same problem. So maybe there's some neat 
solution out there that would solve the issue for both i2c-atr and 
i2c-mux, but it escapes me at the moment.

  Tomi