linux-kernel - Re: [PATCH 5/7] mfd: ds90ux9xx: add I2C bridge/alias and link connection driver

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Date:   Fri, 12 Oct 2018 10:32:32 +0300
From:   Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:     Lee Jones <lee.jones@...aro.org>
CC:     Vladimir Zapolskiy <vz@...ia.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Wolfram Sang <wsa@...-dreams.de>, <devicetree@...r.kernel.org>,
        <linux-gpio@...r.kernel.org>, <linux-media@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/7] mfd: ds90ux9xx: add I2C bridge/alias and link
 connection driver

Hi Lee,

On 10/12/2018 09:04 AM, Lee Jones wrote:
> On Tue, 09 Oct 2018, Vladimir Zapolskiy wrote:
> 
>> From: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
>>
>> The change adds TI DS90Ux9xx I2C bridge/alias subdevice driver and
>> FPD Link connection handling mechanism.
>>
>> Access to I2C devices connected to a remote de-/serializer is done in
>> a transparent way, on established link detection event such devices
>> are registered on an I2C bus, which serves a local de-/serializer IC.
>>
>> The development of the driver was a collaborative work, the
>> contribution done by Balasubramani Vivekanandan includes:
>> * original simplistic implementation of the driver,
>> * support of implicitly specified devices in device tree,
>> * support of multiple FPD links for TI DS90Ux9xx,
>> * other kind of valuable review comments, clean-ups and fixes.
>>
>> Also Steve Longerbeam made the following changes:
>> * clear address maps after linked device removal,
>> * disable pass-through in disconnection,
>> * qualify locked status with non-zero remote address.
>>
>> Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
>> ---
>>  drivers/mfd/Kconfig                |   8 +
>>  drivers/mfd/Makefile               |   1 +
>>  drivers/mfd/ds90ux9xx-i2c-bridge.c | 764 +++++++++++++++++++++++++++++
>>  3 files changed, 773 insertions(+)
>>  create mode 100644 drivers/mfd/ds90ux9xx-i2c-bridge.c
> 
> Shouldn't this live in drivers/i2c?

no, the driver is not for an I2C controller of any kind, and the driver does
not register itself in the I2C subsystem by calling i2c_add_adapter() or
i2c_add_numbered_adapter() or i2c_mux_add_adapter() etc, this topic was
discussed with Wolfram also.

Formally the driver converts the managed IC into a multi-address I2C
slave device, I understand that it does not sound like a well suited driver
for MFD, but ds90ux9xx-core.c and ds90ux9xx-i2c-bridge.c drivers are quite
tightly coupled.

--
Best wishes,
Vladimir