Re: [PATCH V3 02/12] misc: xilinx-sdfec: add core driver

From: Greg KH <gregkh@linuxfoundation.org>
To: Dragan Cvetic <draganc@xilinx.com>
Cc: "arnd@arndb.de" <arnd@arndb.de>,
	Michal Simek <michals@xilinx.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"robh+dt@kernel.org" <robh+dt@kernel.org>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"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
Date: Tue, 7 May 2019 11:39:41 +0200	[thread overview]
Message-ID: <20190507093941.GC20355@kroah.com> (raw)
In-Reply-To: <BL0PR02MB568169E26DCD12498EBDFC3ACB310@BL0PR02MB5681.namprd02.prod.outlook.com>

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-kernel@lists.infradead.org; robh+dt@kernel.org;
> > mark.rutland@arm.com; devicetree@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
> > 
> > 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-kernel@lists.infradead.org; robh+dt@kernel.org;
> > > > mark.rutland@arm.com; devicetree@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
> > > >
> > > > 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-arm-kernel@lists.infradead.org; robh+dt@kernel.org;
> > > > > > mark.rutland@arm.com; devicetree@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
> > > > > >
> > > > > > 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, please 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 and register an instance
> > > > > of that structure associated with a struct file_operations, exposing 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 simpler.
> > > >
> > >
> > > 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 use
> > > class?
> > 
> > Not really :)
> > 
> > 8 devices is pretty small.  What tool will be trying to talk to all of
> > these devices and how was it going to find out what devices were in the
> > 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.

Userspace doesn't mess with DT.

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?

thanks,

greg k-h