linux-kernel - Re: [PATCH v6 3/4] i2c: ch341: add I2C MFD cell driver for the CH341

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Date:   Wed, 15 Jun 2022 22:09:31 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     frank zago <frank@...o.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Wolfram Sang <wsa@...nel.org>, Johan Hovold <johan@...nel.org>,
        linux-usb@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH v6 3/4] i2c: ch341: add I2C MFD cell driver for the CH341

Hi--

On 6/15/22 18:37, frank zago wrote:
> The I2C interface can run at 4 different speeds. This driver currently
> only offer 100kHz. Tested with a variety of I2C sensors, and the IIO
> subsystem.
> 
> Signed-off-by: frank zago <frank@...o.net>
> ---
>  MAINTAINERS                    |   1 +
>  drivers/i2c/busses/Kconfig     |  10 +
>  drivers/i2c/busses/Makefile    |   1 +
>  drivers/i2c/busses/i2c-ch341.c | 377 +++++++++++++++++++++++++++++++++
>  4 files changed, 389 insertions(+)
>  create mode 100644 drivers/i2c/busses/i2c-ch341.c
> 

> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index a1bae59208e3..db9797345ad5 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -1199,6 +1199,16 @@ config I2C_RCAR
>  
>  comment "External I2C/SMBus adapter drivers"
>  
> +config I2C_CH341
> +	tristate "CH341 USB to I2C support"
> +	select MFD_CH341
> +	help
> +	  If you say yes to this option, I2C support will be included for the
> +	  WCH CH341, a USB to I2C/SPI/GPIO interface.
> +
> +	  This driver can also be built as a module.  If so, the module
> +	  will be called i2c-ch341.

I haven't tested it, but just from reading, it looks like
this one needs a "depends on USB" since it selects MFD_CH341, which
depends on USB, and since 'select' ignores dependency chains.

The GPIO driver (patch 2/4) already depends on USB.

-- 
~Randy