linux-kernel - Re: [PATCH 0/3] capebus moving omap

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Message-ID: <20121101220518.GE14982@arwen.pp.htv.fi>
Date:	Fri, 2 Nov 2012 00:05:18 +0200
From:	Felipe Balbi <balbi@...com>
To:	Pantelis Antoniou <panto@...oniou-consulting.com>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>, <balbi@...com>,
	"Cousson, Benoit" <b-cousson@...com>,
	Tony Lindgren <tony@...mide.com>,
	<linux-kernel@...r.kernel.org>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Matt Porter <mporter@...com>, Russ Dill <Russ.Dill@...com>,
	<linux-omap@...r.kernel.org>, Kevin Hilman <khilman@...com>,
	Paul Walmsley <paul@...an.com>
Subject: Re: [PATCH 0/3] capebus moving omap_devices to mach-omap2

HI,

On Thu, Nov 01, 2012 at 03:59:50PM +0200, Pantelis Antoniou wrote:
> Hi Alan,
> 
> On Nov 1, 2012, at 3:51 PM, Alan Cox wrote:
> 
> >> What they want, and what every user wants, is I plug this board in, and
> >> the driver make sure everything is loaded and ready. No, the end users
> >> don't want to see any of the implementation details of how the bitfile
> >> is transported; the driver can handle it.
> > 
> > That doesn't necessarily make it a bus merely some kind of hotplug
> > enumeration of devices. That should all work properly both for devices
> > and busses with spi and i²c as the final bits needed for it got fixed
> > some time ago.
> > 
> > In an ideal world you don't want to be writing custom drivers for stuff.
> > If your cape routes an i²c serial device to the existing system i²c
> > busses then you want to just create an instance of any existing driver on
> > the existing i²c bus not create a whole new layer of goop.
> > 
> > It does need to do the plumbing and resource management for the plumbing
> > but thats not the same as being a bus.
> > 
> > Alan
> 
> 
> Fair enough. But there's no such thing a 'hotplug enumeration
> construct' in Linux yet, and a bus is the closest thing to it. It does
> take advantage of the nice way device code matches drivers and devices
> though.
> 
> I'm afraid that having the I2C/SPI drivers doing the detection won't
> work.  The capes can have arbitrary I2C/SPI devices (and even more
> weird components).  There is no way to assure for example that the I2C
> device responding to address 'foo' in cape A is the same I2C device
> responding to the same address in cape B.

your ->detect() method should take care of that.

-- 
balbi

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