linux-kernel - Re: [PATCH misc v2 2/2] misc: Add Renesas Synchronization Management Unit (SMU) support

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Message-ID: <YUNrPD5pbq5NBi26@kroah.com>
Date:   Thu, 16 Sep 2021 18:05:16 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Min Li <min.li.xe@...esas.com>
Cc:     "arnd@...db.de" <arnd@...db.de>,
        "derek.kiernan@...inx.com" <derek.kiernan@...inx.com>,
        "dragan.cvetic@...inx.com" <dragan.cvetic@...inx.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "lee.jones@...aro.or" <lee.jones@...aro.or>
Subject: Re: [PATCH misc v2 2/2] misc: Add Renesas Synchronization Management
 Unit (SMU) support

On Thu, Sep 16, 2021 at 03:54:52PM +0000, Min Li wrote:
> > 
> > Please put that link in the changelog comment and in the .c code as well so
> > that people know where to find it.
> > 
> > > >
> > > > 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
> > 
> > Then make one!  :)
> 
> Yes it is on our roadmap to do that for next release

Please do it for this kernel api, otherwise you have to support this for
the next 20+ years as-is :(

> > 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?
> > 
> We used to do everything in userspace. But since PHC (ptp hardware clock) came along, we decided
> to move the driver part to kernel. Please take a look at drivers/ptp/ptp_clockmatrix.c for reference.
> Recently, we have some functions like APTS that doesn't belong to PTP or anything else so we have to split those functions
> to RSMU misc driver and i2c/spi bus accesses to RSMU MFD driver.

I still do not understand why this has to be a kernel driver, sorry.
What exactly forces it to be that way?

thanks,

greg k-h