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

[Ye, Xiang]

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@xxxxxxxxx>
> > Reviewed-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > ---
> >  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