linux-kernel - Re: [PATCH 4/7] mfd: ds90ux9xx: add TI DS90Ux9xx de-/serializer MFD driver

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Date:   Fri, 12 Oct 2018 10:41:20 +0300
From:   Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:     Lee Jones <lee.jones@...aro.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     Vladimir Zapolskiy <vz@...ia.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Marek Vasut <marek.vasut@...il.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 4/7] mfd: ds90ux9xx: add TI DS90Ux9xx de-/serializer MFD
 driver

Hi Lee,

On 10/12/2018 09:03 AM, Lee Jones wrote:
> On Tue, 09 Oct 2018, Vladimir Zapolskiy wrote:
> 
>> From: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
>>
>> The change adds I2C device driver for TI DS90Ux9xx de-/serializers,
>> support of subdevice controllers is done in separate drivers, because
>> not all IC functionality may be needed in particular situations, and
>> this can be fine grained controlled in device tree.
>>
>> The development of the driver was a collaborative work, the
>> contribution done by Balasubramani Vivekanandan includes:
>> * original implementation of the driver based on a reference driver,
>> * regmap powered interrupt controller support on serializers,
>> * support of implicitly or improperly specified in device tree ICs,
>> * support of device properties and attributes: backward compatible
>>   mode, low frequency operation mode, spread spectrum clock generator.
>>
>> Contribution by Steve Longerbeam:
>> * added ds90ux9xx_read_indirect() function,
>> * moved number of links property and added ds90ux9xx_num_fpd_links(),
>> * moved and updated ds90ux9xx_get_link_status() function to core driver,
>> * added fpd_link_show device attribute.
>>
>> Sandeep Jain added support of pixel clock edge configuration.
>>
>> Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
>> ---
>>  drivers/mfd/Kconfig           |  14 +
>>  drivers/mfd/Makefile          |   1 +
>>  drivers/mfd/ds90ux9xx-core.c  | 879 ++++++++++++++++++++++++++++++++++
>>  include/linux/mfd/ds90ux9xx.h |  42 ++
>>  4 files changed, 936 insertions(+)
>>  create mode 100644 drivers/mfd/ds90ux9xx-core.c
>>  create mode 100644 include/linux/mfd/ds90ux9xx.h
>>
>> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
>> index 8c5dfdce4326..a969fa123f64 100644
>> --- a/drivers/mfd/Kconfig
>> +++ b/drivers/mfd/Kconfig
>> @@ -1280,6 +1280,20 @@ config MFD_DM355EVM_MSP
>>  	  boards.  MSP430 firmware manages resets and power sequencing,
>>  	  inputs from buttons and the IR remote, LEDs, an RTC, and more.
>>  
>> +config MFD_DS90UX9XX
>> +	tristate "TI DS90Ux9xx FPD-Link de-/serializer driver"
>> +	depends on I2C && OF
>> +	select MFD_CORE
>> +	select REGMAP_I2C
>> +	help
>> +	  Say yes here to enable support for TI DS90UX9XX de-/serializer ICs.
>> +
>> +	  This driver provides basic support for setting up the de-/serializer
>> +	  chips. Additional functionalities like connection handling to
>> +	  remote de-/serializers, I2C bridging, pin multiplexing, GPIO
>> +	  controller and so on are provided by separate drivers and should
>> +	  enabled individually.
> 
> This is not an MFD driver.

Why do you think so? The representation of the ICs into device tree format
of hardware description shows that this is a truly MFD driver with multiple
IP subcomponents naturally mapped into MFD cells.

Basically it is possible to replace explicit of_platform_populate() by
adding a "simple-mfd" compatible, if it is desired.

> After a 30 second Google of what this device actually does, perhaps
> drivers/media might be a better fit?
> 

I assume it would be quite unusual to add a driver with NO media functions
and controls into drivers/media.

Laurent, can you please share your opinion?

--
Best wishes,
Vladimir