Re: [PATCH v4 0/8] i2c-atr and FPDLink

From: "Vaittinen, Matti" <Matti.Vaittinen@fi.rohmeurope.com>
To: Luca Ceresoli <luca.ceresoli@bootlin.com>,
	Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Cc: "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
	Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	Jacopo Mondi <jacopo@jmondi.org>,
	Kieran Bingham <kieran.bingham@ideasonboard.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Luca Ceresoli <luca@lucaceresoli.net>,
	Mark Rutland <mark.rutland@arm.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Peter Rosin <peda@axentia.se>, Rob Herring <robh+dt@kernel.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Vladimir Zapolskiy <vz@mleia.com>,
	Wolfram Sang <wsa@the-dreams.de>,
	"satish.nagireddy@getcruise.com" <satish.nagireddy@getcruise.com>
Subject: Re: [PATCH v4 0/8] i2c-atr and FPDLink
Date: Mon, 7 Nov 2022 12:12:29 +0000	[thread overview]
Message-ID: <8abbf9fd-8bcb-f82e-5632-0267e79c3850@fi.rohmeurope.com> (raw)
In-Reply-To: <20221107124814.19b12473@booty>

On 11/7/22 13:48, Luca Ceresoli wrote:
> Hi Tomi, All,
> 
> On Tue,  1 Nov 2022 15:20:24 +0200
> Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> wrote:
>>
>> 2)
>> If I suggested adding an i2c-bus fwnode parameter to
>> i2c_mux_add_adapter(), and the i2c-bus might be under some other device,
>> I think the reception could be quite negative (and I would agree). For
>> this reason I'm not very happy with the i2c-atr and using it with
>> FPDLink.
>>
>> In fact, I'm thinking that it might be better to just drop the i2c-atr
>> driver, and add the support directly to the FPDlink drivers. But that
>> could mean possibly duplicating the same code for other deser/ser
>> architectures, so I have kept the i2c-atr driver for now.
> 
> Indeed I think the ROHM serdes chips do have an address translation
> feature that works pretty much like the TI ones, and the ATR should be
> cleanly reusable across the two brands. The ATR code might be
> simplified to just provide helpers for common code maybe, but I'd
> rather avoid code duplication.

I tend to agree with Luca on keeping the I2C-atr a re-usable generic 
code. The reason why I did not (yet) bring this (or other concerns) up 
is that currently I don't have a permission to upstream my work for ROHM 
SerDes Linux drivers :( I still do discuss the decision but to be 
honest, I believe the chances to get my drivers upstream are getting 
slim. Hence I did not see it reasonable to try pushing Tomi's / Luca's 
work to any direction.

Yet, after that being said - these SerDes devices which can combine I2C 
buses from multiple remote devices to one local I2C controller do bring 
a real need for a solution like the address translation. Thus, I would 
not be surprized if we saw new devices with this kind of feature. 
Potentially also from other vendors. So, regardless what happens with 
ROHM SERDESes - I (too) think we should keep the ATR as independently 
reusable component.

Yours,
	-- Matti Vaittinen

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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