linux-kernel - Re: [PATCH] spi: reorganize drivers

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Date:	Mon, 6 Jun 2011 17:04:27 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	Jean Delvare <khali@...ux-fr.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	"Ben Dooks (embedded platforms)" <ben-linux@...ff.org>,
	linux-pcmcia@...ts.infradead.org,
	Matt Porter <mporter@...nel.crashing.org>,
	Alexandre Bounine <alexandre.bounine@....com>,
	"David S. Miller" <davem@...emloft.net>,
	Michael Buesch <mb@...sch.de>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Florian Fainelli <florian@...nwrt.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	spi-devel-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH] spi: reorganize drivers

On Monday 06 June 2011, Stefan Richter wrote:
> On Jun 06 Arnd Bergmann wrote:
> > On Monday 06 June 2011, Jean Delvare wrote:
> On drivers/firewire/:
> 
> FireWire drivers are currently spread over drivers/firewire (three
> link-layer controller drivers + the IEEE 1394 core + two IEEE 1394
> application layer drivers), drivers/media/dvb/firewire/ (one 1394
> application layer driver), sound/firewire/ (two 1394 application layer
> drivers, more are planned to be added there).
> 
> From the Linux driver model POV,
>   1. the IEEE 1394 core driver implements the firewire bus,
>   2. the link-layer controller drivers implement pci bus based devices,
>   3. the IEEE 1394 application layer drivers implement firewire bus based
>      devices.  The two of them that are located in drivers/firewire/
>      expose a SCSI LLD (a transport in SCSI Architecture Model terms, but
>      a host rather than a transport in Linux implementation terms) and a
>      networking interface driver.
> 
> Number 2 is something one would expect to find in a hypothetical
> drivers/bus/ directory.  But where do the others belong?
> 
> Would type 1 drivers be kept in drivers/bus/firewire/?  I understand your
> above response to Jean that this is what you have in mind.

Correct.

> firewire-sbp2 could be moved into drivers/scsi/, and firewire-net could be
> moved into drivers/net/.  But what about maintenance?  They could still be
> maintained via linux1394-2.6.git because this worked so far, but then the
> directory structure might irritate people who don't use
> scripts/get_maintainer.pl all the time.  Well, I could actually picture
> firewire-net to be maintained via the net development tree, but I do
> wonder how well firewire-sbp2 maintenance through the scsi tree would work.

I guess the real question is whether firewire should be considered a bus
like USB or a device class like SCSI, and it's abit of a grey area (SCSI
is too). If you declare it to be a bus, I'd suggest moving the sbp2 and
network drivers to drivers/scsi and drivers/net. If you like to think
of firewire as a closed subsystem instead, it's probably better to leave
all of it in drivers/firewire.

> PS,
> these are the same questions like with USB, only on a smaller scale.  (The
> usb-storage driver is maintained through the usb tree as well, not the
> scsi tree.  drivers/net/usb/ has got T: git .../gregkh/usb-2.6.git
> assigned in MAINTAINERS but most of the commits there are actually done by
> DaveM.)

The difference that I see with usb-storage is that this one is really
a set of different drivers for all sorts of devices, while the firewire sbp2
driver feels more like a single driver that includes a few special
cases. Also, USB is generally perceived as a generic interconnect, while
firewire is seen primarily as a way to attach disk drives.

The differences are of course gradual.

	Arnd
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