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Date:   Wed, 15 Sep 2021 16:46:06 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Min Li <min.li.xe@renesas.com>
Cc:     "derek.kiernan@xilinx.com" <derek.kiernan@xilinx.com>,
        "dragan.cvetic@xilinx.com" <dragan.cvetic@xilinx.com>,
        "arnd@arndb.de" <arnd@arndb.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH misc] misc: Add Renesas Synchronization Management Unit
 (SMU) support
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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