linux-kernel - Re: [PATCH v2 3/4] switchtec: Add sysfs attributes to the Switchtec driver

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Message-ID: <20170224224527.GC26430@bhelgaas-glaptop.roam.corp.google.com>
Date:   Fri, 24 Feb 2017 16:45:27 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Keith Busch <keith.busch@...el.com>,
        Myron Stowe <myron.stowe@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Jonathan Corbet <corbet@....net>,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        Wei Zhang <wzhang@...com>,
        Kurt Schwemmer <kurt.schwemmer@...rosemi.com>,
        Stephen Bates <stephen.bates@...rosemi.com>,
        linux-pci@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] switchtec: Add sysfs attributes to the Switchtec
 driver

On Thu, Feb 23, 2017 at 03:56:21PM -0700, Logan Gunthorpe wrote:
> 
> 
> On 23/02/17 03:43 PM, Bjorn Helgaas wrote:
> > This path seems a little generic.  I don't see other cases where a
> > product brand name ("Switchtec") appears at the top level of
> > /sys/class/...
> 
> Ok, well we are certainly open to suggestions, but there isn't really a
> generic version of this device available so I'm not sure how we would
> change that. Per device-type classes aren't that uncommon though, a
> quick grep shows things like:
> 
> platform/chrome/cros_ec_dev.c:40:static struct class cros_class
> s390/char/raw3270.h:94:extern struct class *class3270;
> net/ethernet/hisilicon/hns/hnae.c:19:static struct class *hnae_class;
> mfd/ucb1x00-core.c:490:static struct class ucb1x00_class
> 
> > My question is based on "ls Documentation/ABI/testing/sysfs-class*",
> > not on any great knowledge of sysfs, and I see Greg has already given
> > a Reviewed-by for this, so maybe this is the right approach.
> > 
> > It does seem like the path could include a clue that this is related
> > to PCI.
> 
> I mean, we could change it to pci-switchtec or something if you think
> that would be better..?? But I'm not sure how else to accommodate this.

I'm OK with it as-is.

> > Is there a link to the switch PCI device itself, e.g., to
> > /sys/devices/pci*?  Should these attributes simply be put in a
> > subdirectory there, e.g., in
> > 
> >   /sys/devices/pci0000:00/0000:00:00.0/stats/...
> 
> Well our device shows up here in the tree:
> 
> /sys/devices/pci0000:00/0000:00:03.0/0000:03:00.1/switchtec/switchtec0
> 
> (Which userspace can get to by following the link at
> /sys/class/switchtec/switchtec0) The switch is then always:
> 
> /sys/devices/pci0000:00/0000:00:03.0

That's exactly what I was looking for; I just didn't realize it was
connected like this.

Bjorn