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From:   Min Li <min.li.xe@renesas.com>
To:     Greg KH <gregkh@linuxfoundation.org>
CC:     "arnd@arndb.de" <arnd@arndb.de>,
        "derek.kiernan@xilinx.com" <derek.kiernan@xilinx.com>,
        "dragan.cvetic@xilinx.com" <dragan.cvetic@xilinx.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "lee.jones@linaro.or" <lee.jones@linaro.or>
Subject: RE: [PATCH misc v2 2/2] misc: Add Renesas Synchronization Management
 Unit (SMU) support
Thread-Topic: [PATCH misc v2 2/2] misc: Add Renesas Synchronization Management
 Unit (SMU) support
Thread-Index: AQHXqmIqGzfEPA/ASUKU/78egiaTO6umId8AgACkSYCAAAc7gIAAAX9g
Date:   Thu, 16 Sep 2021 15:54:52 +0000
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>=20
> Please put that link in the changelog comment and in the .c code as well =
so
> that people know where to find it.
>=20
> > >
> > > Why is this new api not a standard one?
> > >
> >
> > There is no actual standard for the GNSS assisted partial timing
> > support (APTS) In terms of Linux kernel API
>=20
> Then make one!  :)

Yes it is on our roadmap to do that for next release

>=20
> > > What is the standard here?
> > >
> > > What do other devices do and why is this a new api?
> > >
> >
> > There is really no standard for APTS and different company has its own
> > hw/sw solutions
>=20
> But userspace has to all deal with this in a standard way somehow, right?
> What libraries and apis do they interact with there?

So far there is none. Some companies just use userspace driver and don't bo=
ther
kernel

>=20
> > > > Current version provides kernel API's to support the following
> > > > functions -set combomode to enable SYNCE clock support -read
> > > > dpll's state to determine if the dpll is locked to the GNSS
> > > > channel -read dpll's ffo (fractional frequency offset) in ppqt
> > >
> > > Why do all of these have to be in the kernel at all?
> > >
> >
> > Because all these API's need spi/i2c accesses to the RSMU card and
> > spi/i2c accesses have been abstracted to the MFD driver in kernel
>=20
> Why not just do this all from userspace then?  You can have spi/i2c
> userspace code, right?  Why does this have to be a kernel driver?
>=20
We used to do everything in userspace. But since PHC (ptp hardware clock) c=
ame along, we decided
to move the driver part to kernel. Please take a look at drivers/ptp/ptp_cl=
ockmatrix.c for reference.
Recently, we have some functions like APTS that doesn't belong to PTP or an=
ything else so we have to split those functions
to RSMU misc driver and i2c/spi bus accesses to RSMU MFD driver.