linux-kernel - Re: [PATCH v4 1/5] mfd: Add support for Intel LJCA device

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Date:   Thu, 9 Mar 2023 18:00:57 +0800
From:   "Ye, Xiang" <xiang.ye@...el.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Lee Jones <lee@...nel.org>, Wolfram Sang <wsa@...nel.org>,
        Tyrone Ting <kfting@...oton.com>,
        Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        "Bartosz Golaszewski" <brgl@...ev.pl>, <linux-usb@...r.kernel.org>,
        <linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-spi@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
        <srinivas.pandruvada@...el.com>, <heikki.krogerus@...ux.intel.com>,
        <andriy.shevchenko@...ux.intel.com>,
        <sakari.ailus@...ux.intel.com>, <zhifeng.wang@...el.com>,
        <wentong.wu@...el.com>, <lixu.zhang@...el.com>
Subject: Re: [PATCH v4 1/5] mfd: Add support for Intel LJCA device

Hi Arnd,

Thanks for the review.
On Thu, Mar 09, 2023 at 08:56:05AM +0100, Arnd Bergmann wrote:
> On Thu, Mar 9, 2023, at 08:10, Ye Xiang wrote:
> 
> > The minimum code in ASL that covers this board is
> > Scope (\_SB.PCI0.DWC3.RHUB.HS01)
> >     {
> >         Device (GPIO)
> >         {
> >             Name (_ADR, Zero)
> >             Name (_STA, 0x0F)
> >         }
> >
> >         Device (I2C)
> >         {
> >             Name (_ADR, One)
> >             Name (_STA, 0x0F)
> >         }
> >
> >         Device (SPI)
> >         {
> >             Name (_ADR, 0x02)
> >             Name (_STA, 0x0F)
> >         }
> >     }
> 
> I'm a bit confused by this bit, does that mean this only works
> if the device is integrated on the mainboard and the BIOS is
> aware of it? This won't work if  you plug it into a random
> USB port, or have no ACPI firmware, right?
LJCA can work both when there is an ACPI firmware or not.

When there is a config like "The minimum code in ASL" in DSDT, LJCA device and
its sub-devices will bind to right ACPI devices. Our current use case needs the
the ACPI binding. Because we have a camera sensor depending on this LJCA device,
We use the ACPI binding to control the probe order, making sure the camera
sensor probe after LJCA and LJCA-I2C.

When there isn't a config in DSDT, the LJCA device also can works. But
it won't have an acpi binding.

So, If you plug into a random USB port or have no ACPI binding, It just
does not have an ACPI binding.
> 
> > Signed-off-by: Ye Xiang <xiang.ye@...el.com>
> > Reviewed-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> > ---
> >  drivers/usb/misc/Kconfig  |  13 +
> >  drivers/usb/misc/Makefile |   1 +
> >  drivers/usb/misc/ljca.c   | 969 ++++++++++++++++++++++++++++++++++++++
> >  include/linux/mfd/ljca.h  |  95 ++++
> 
> Why is this in driver/usb/misc? It looks like a normal
> mfd driver to me, and it evenhas the header in include/linux/mfd/
It's a mistake. I just moved it from driver/mfd and forget to move the header to right place.
It will be addressed on next version. 
> 
>      Arnd

--
Thanks
Ye Xiang