linux-kernel - Re: [PATCH v2] arch/tile: add hypervisor-based character driver for SPI flash ROM

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Date:	Sun, 29 May 2011 08:18:36 -0400
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Greg KH <gregkh@...e.de>
CC:	<linux-kernel@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
	Eric Biederman <ebiederm@...stanetworks.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Benjamin Thery <benjamin.thery@...l.net>,
	Phil Carmody <ext-phil.2.carmody@...ia.com>
Subject: Re: [PATCH v2] arch/tile: add hypervisor-based character driver for
 SPI flash ROM

On 5/29/2011 7:45 AM, Greg KH wrote:
> On Sat, May 28, 2011 at 08:32:07PM -0400, Chris Metcalf wrote:
>>> As you are only using 1 minor device, why not just use a misc device
>>> instead?  It's simpler, and you get the sysfs code for free, which you
>>> forgot to do, so your device node will never show up in userspace :(
>> Interesting; this appears to be a bug.  We use 4 minors (see "srom_devs =
>> 4" higher up).  I'll fix this.  We may have some other devices that would
>> benefit from being recast as misc devices, so I'll look at our set of
>> internal devices.
> This kind of implies that you didn't test this code, right?  You might
> want to do that next time :)

No, this bug has been in the code since day one (I just double-checked our
SCM), and it has always worked fine.  I'm looking into how this is possible
now, but trust me, we've tested this aspect of the driver the whole time. :-)

>> Is there a good example of a character device that has multiple minors and
>> also is registered with sysfs?
> Lots of them, look all over the kernel, and in LDD3 there's even an
> outdated example of one I think.

 I didn't actually find many drivers that have both cdev_add with count>1,
and mention sysfs or kobj, but char/raw.c is one that looks pretty clean. 
(I found only four others total: uio/uio.c, s390/char/vmlogrdr.c,
staging/comedi/comedi_fops.c, and staging/vme/devices/vme_user.c.)

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com


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