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From:   Dragan Cvetic <draganc@xilinx.com>
To:     Greg KH <gregkh@linuxfoundation.org>
CC:     "arnd@arndb.de" <arnd@arndb.de>, Michal Simek <michals@xilinx.com>,
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        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Derek Kiernan <dkiernan@xilinx.com>
Subject: RE: [PATCH V3 02/12] misc: xilinx-sdfec: add core driver
Thread-Topic: [PATCH V3 02/12] misc: xilinx-sdfec: add core driver
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Date:   Tue, 7 May 2019 11:55:42 +0000
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> -----Original Message-----
> From: Greg KH [mailto:gregkh@linuxfoundation.org]
> Sent: Tuesday 7 May 2019 10:40
> To: Dragan Cvetic <draganc@xilinx.com>
> Cc: arnd@arndb.de; Michal Simek <michals@xilinx.com>; linux-arm-kernel@li=
sts.infradead.org; robh+dt@kernel.org;
> mark.rutland@arm.com; devicetree@vger.kernel.org; linux-kernel@vger.kerne=
l.org; Derek Kiernan <dkiernan@xilinx.com>
> Subject: Re: [PATCH V3 02/12] misc: xilinx-sdfec: add core driver
>=20
> On Tue, May 07, 2019 at 08:48:41AM +0000, Dragan Cvetic wrote:
> >
> >
> > > -----Original Message-----
> > > From: Greg KH [mailto:gregkh@linuxfoundation.org]
> > > Sent: Monday 6 May 2019 13:34
> > > To: Dragan Cvetic <draganc@xilinx.com>
> > > Cc: arnd@arndb.de; Michal Simek <michals@xilinx.com>; linux-arm-kerne=
l@lists.infradead.org; robh+dt@kernel.org;
> > > mark.rutland@arm.com; devicetree@vger.kernel.org; linux-kernel@vger.k=
ernel.org; Derek Kiernan <dkiernan@xilinx.com>
> > > Subject: Re: [PATCH V3 02/12] misc: xilinx-sdfec: add core driver
> > >
> > > On Mon, May 06, 2019 at 12:23:56PM +0000, Dragan Cvetic wrote:
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Greg KH [mailto:gregkh@linuxfoundation.org]
> > > > > Sent: Saturday 4 May 2019 08:55
> > > > > To: Dragan Cvetic <draganc@xilinx.com>
> > > > > Cc: arnd@arndb.de; Michal Simek <michals@xilinx.com>; linux-arm-k=
ernel@lists.infradead.org; robh+dt@kernel.org;
> > > > > mark.rutland@arm.com; devicetree@vger.kernel.org; linux-kernel@vg=
er.kernel.org; Derek Kiernan <dkiernan@xilinx.com>
> > > > > Subject: Re: [PATCH V3 02/12] misc: xilinx-sdfec: add core driver
> > > > >
> > > > > On Fri, May 03, 2019 at 04:41:21PM +0000, Dragan Cvetic wrote:
> > > > > > Hi Greg,
> > > > > >
> > > > > > Please find my inline comments below,
> > > > > >
> > > > > > Regards
> > > > > > Dragan
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Greg KH [mailto:gregkh@linuxfoundation.org]
> > > > > > > Sent: Thursday 2 May 2019 18:20
> > > > > > > To: Dragan Cvetic <draganc@xilinx.com>
> > > > > > > Cc: arnd@arndb.de; Michal Simek <michals@xilinx.com>; linux-a=
rm-kernel@lists.infradead.org; robh+dt@kernel.org;
> > > > > > > mark.rutland@arm.com; devicetree@vger.kernel.org; linux-kerne=
l@vger.kernel.org; Derek Kiernan <dkiernan@xilinx.com>
> > > > > > > Subject: Re: [PATCH V3 02/12] misc: xilinx-sdfec: add core dr=
iver
> > > > > > >
> > > > > > > On Sat, Apr 27, 2019 at 11:04:56PM +0100, Dragan Cvetic wrote=
:
> > > > > > > > +#define DRIVER_NAME "xilinx_sdfec"
> > > > > > > > +#define DRIVER_VERSION "0.3"
> > > > > > >
> > > > > > > Version means nothing with the driver in the kernel tree, ple=
ase remove
> > > > > > > it.
> > > > > >
> > > > > > Will be removed. Thank you.
> > > > > >
> > > > > > >
> > > > > > > > +#define DRIVER_MAX_DEV BIT(MINORBITS)
> > > > > > >
> > > > > > > Why this number?  Why limit yourself to any number?
> > > > > > >
> > > > > >
> > > > > > There can be max 8 devices for this driver. I'll change to 8.
> > > > > >
> > > > > > > > +
> > > > > > > > +static struct class *xsdfec_class;
> > > > > > >
> > > > > > > Do you really need your own class?
> > > > > >
> > > > > > When writing a character device driver, my goal is to create an=
d register an instance
> > > > > > of that structure associated with a struct file_operations, exp=
osing a set of operations
> > > > > > to the user-space. One of the steps to make this goal is Create=
 a class for a devices,
> > > > > > visible in /sys/class/.
> > > > >
> > > > > Why do you need a class?  Again, why not just use the misc_device=
 api,
> > > > > that seems much more relevant here and will make the code a lot s=
impler.
> > > > >
> > > >
> > > > The driver can have 8 devices in SoC plus more in Programming Logic=
.
> > > > It looked logical to group them under the same MAJOR, although they
> > > > are independent of each other.  Is this argument strong enough to u=
se
> > > > class?
> > >
> > > Not really :)
> > >
> > > 8 devices is pretty small.  What tool will be trying to talk to all o=
f
> > > these devices and how was it going to find out what devices were in t=
he
> > > system?
> > >
> >
> > These devices are Forward Error Correction encoder/decoder
> > and will be part of the RF communication chain. They will be included
> > in the system through DT. Also, described in DT.
>=20
> Userspace doesn't mess with DT.
>=20
> I am asking what userspace tool/program is going to be interacting with
> these devices through your now-custom api you are creating.  Do you have
> a link to that software, and how is that code doing the "determine what
> device nodes are associated with what devices" logic?
>=20

Example code is not public yet, sorry. The index number in the device name
is a link to device, see snippet from the example code:

#define FEC_DEC  "/dev/xsdfec0"
dec_fd =3D open_xsdfec(FEC_DEC);

The index number corresponds to the device order in DT.

> thanks,
>=20
> greg k-h