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

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Date:   Wed, 15 Sep 2021 15:00:15 +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

> On Wed, Sep 15, 2021 at 02:42:55PM +0000, Min Li wrote:
> > > > > > +/*
> > > > > > + * 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.
> 
> Why not work on a real set of apis for this type of thing so that all devices of
> this type will work properly?
> 
> thanks,
> 
> greg k-h

Hi Greg

That plan is on our roadmap. On the other hand, this is a new area that different company has its
own hw/sw solution and it takes time to abstract functions to kernel. Also, our APTS first release
was already out. Right now we are actively developing another release that we will try out best to
come up with better solution.