linux-kernel - RE: [PATCH misc] misc: Add Renesas Synchronization Management Unit (SMU) support

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Date:   Wed, 15 Sep 2021 14:42:55 +0000
From:   Min Li <min.li.xe@...esas.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "derek.kiernan@...inx.com" <derek.kiernan@...inx.com>,
        "dragan.cvetic@...inx.com" <dragan.cvetic@...inx.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH misc] misc: Add Renesas Synchronization Management Unit
 (SMU) support

> > > > +/*
> > > > + * RSMU IOCTL List
> > > > + */
> > > > +#define RSMU_MAGIC '?'
> > >
> > > Where did you get this value from?
> > >
> > > Where did you reserve it?
> >
> > No I didn't reserve it. I checked other code and they all seem to use
> > a random character
> 
> That's not the best way to do this.
> 
> Why do you need ioctls at all anyway?  What userspace tools will be
> accessing this driver?  Do you have a link to where they are located at?

Hi Greg

The userspace tool is called PCM4L (PTP Clock Manager for Linux) from Renesas

https://www.renesas.com/us/en/software-tool/ptp-clock-manager-linux

But the functions of this misc driver is not ptp related. It is meant for being called by pcm4l to
support GNSS assisted partial timing support (APTS), which doesn't have abstracted/dedicated
Linux Kernel API's. That is why I went for IOCTL in the first place.

Thanks

Min