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Date:	Mon, 1 Sep 2014 13:22:53 +0300
From:	Octavian Purdila <octavian.purdila@...el.com>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>, wsa@...-dreams.de,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Arnd Bergmann <arnd@...db.de>, Johan Hovold <johan@...nel.org>,
	linux-usb@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org,
	Daniel Baluta <daniel.baluta@...el.com>,
	Laurentiu Palcu <laurentiu.palcu@...el.com>
Subject: Re: [PATCH v2 1/3] mfd: add support for Diolan DLN-2 devices

On Mon, Sep 1, 2014 at 12:51 PM, Lee Jones <lee.jones@...aro.org> wrote:
> On Mon, 01 Sep 2014, Octavian Purdila wrote:
>
>> On Mon, Sep 1, 2014 at 11:37 AM, Lee Jones <lee.jones@...aro.org> wrote:
>> > On Sat, 30 Aug 2014, Octavian Purdila wrote:
>> >
>> >> This patch implements the USB part of the Diolan USB-I2C/SPI/GPIO
>> >> Master Adapter DLN-2. Details about the device can be found here:
>> >>
>> >> https://www.diolan.com/i2c/i2c_interface.html.
>> >>
>> >> Information about the USB protocol can be found in the Programmer's
>> >> Reference Manual [1], see section 1.7.
>> >>
>> >> Because the hardware has a single transmit endpoint and a single
>> >> receive endpoint the communication between the various DLN2 drivers
>> >> and the hardware will be muxed/demuxed by this driver.
>> >>
>> >> Each DLN2 module will be identified by the handle field within the DLN2
>> >> message header. If a DLN2 module issues multiple commands in parallel
>> >> they will be identified by the echo counter field in the message header.
>> >>
>> >> The DLN2 modules can use the dln2_transfer() function to issue a
>> >> command and wait for its response. They can also register a callback
>> >> that is going to be called when a specific event id is generated by
>> >> the device (e.g. GPIO interrupts). The device uses handle 0 for
>> >> sending events.
>> >>
>> >> [1] https://www.diolan.com/downloads/dln-api-manual.pdf
>> >
>> > MFD is not a dumping ground for misfit h/w.  Almost all of this code
>> > looks like it belongs in drivers/usb.  Please move it there.
>> >
>>
>> We initially submitted this driver as a pure USB driver, with our own
>> module registration mechanism, but during the first round of reviews
>> people pointed out that a MFD driver is the better approach, and I
>> agree. I also see that there are already a couple of USB drivers
>> implemented as MFD drivers.
>
> Can you link me to your previous submission please?

Sure, here it is:

https://lkml.org/lkml/2014/8/20/228

>
>> Do you see a better approach?
>
> You should have a small MFD driver which controls resources and
> registers children.  All other functionality should live in their
> respective drivers/X locations i.e. USB functionallity should normally
> live in drivers/usb.
>

OK, that sounds better. I am not sure how to handle the registration
part though, since in this case we need to create the children at
runtime, from the usb probe routine.

The only solution I see is to move the driver completely to
usb/drivers and continue to use the MFD infrastructure. Does that
sound OK to you?

Thanks,
Tavi
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