Date:   Tue, 14 Mar 2023 23:38:14 +0800
From:   "Ye, Xiang" <xiang.ye@intel.com>
To:     Heikki Krogerus <heikki.krogerus@linux.intel.com>
CC:     Lee Jones <lee@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Matthias Kaehlcke" <mka@chromium.org>,
        Wolfram Sang <wsa@kernel.org>,
        Tyrone Ting <kfting@nuvoton.com>,
        Mark Brown <broonie@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <brgl@bgdev.pl>,
        <linux-usb@vger.kernel.org>, <linux-i2c@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-spi@vger.kernel.org>,
        <linux-gpio@vger.kernel.org>, <srinivas.pandruvada@intel.com>,
        <andriy.shevchenko@linux.intel.com>,
        <sakari.ailus@linux.intel.com>, <zhifeng.wang@intel.com>,
        <wentong.wu@intel.com>, <lixu.zhang@intel.com>
Subject: Re: [PATCH v5 1/5] usb: Add support for Intel LJCA device
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Hi Heikki,

Thanks for the review.
On Tue, Mar 14, 2023 at 10:36:57AM +0200, Heikki Krogerus wrote:
> Hi Xiang,
> 
> On Tue, Mar 14, 2023 at 04:03:26PM +0800, Ye, Xiang wrote:
> > > Please don't use the MFD API outside of drivers/mfd.
> > > 
> > > If you wish to use the API, please do.
> > > 
> > > Strip out (only) the MFD parts and move them into drivers/mfd.
> > I have no idea about how to split MFD parts out from this driver
> > currently. The MFD part just have mfd cells filling and the call
> > mfd_add_hotplug_devices to register mfd devices. How to module them
> > as an independent driver?
> > Would you give some hints or recommendations?
> > 
> > And I am a little comfused about where this USB device driver should
> > be put to (drivers/mfd or drivers/usb).
> > 
> > As far as I know, where a driver should be put is based on what
> > it provides. This driver just do some urb package transfer to provides
> > multi-functions, such as GPIO function, I2C function, SPI function.
> > so it should be under drivers/mfd folder. Please correct me, if
> > something is wrong. Thanks
> 
> You don't really seem to get any benefit from MFD. Perhaps it would be
> more appropriate and clear if you just registered auxiliary devices in
> this driver. Check drivers/base/auxiliary.c.
Yes, it should be a work. I have a question.
MFD provides the ACPI binding for sub-devices through
struct mfd_cell_acpi_match. But I didn't see this in drivers/base/auxiliary.c.
If using auxiliary bus to implement the LJCA sub-devices, we need to do
the sub-devices acpi binding manually in ljca.c.

Something Like:
adr = LJCA_ACPI_MATCH_GPIO
adev = acpi_find_child_device(parent, adr, false);
ACPI_COMPANION_SET(&pdev->dev, adev ?: parent);

Is that acceptable?

--
Thanks
Ye Xiang