linux-kernel - Re: [PATCH 04/30] staging/vme: allow non-dynamic allocation of bus numbers

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Message-ID: <20101027151327.GR10869@flamenco.cs.columbia.edu>
Date:	Wed, 27 Oct 2010 11:13:27 -0400
From:	"Emilio G. Cota" <cota@...ap.org>
To:	Martyn Welch <martyn.welch@...com>
Cc:	Greg KH <greg@...ah.com>, LKML <linux-kernel@...r.kernel.org>,
	devel@...verdev.osuosl.org,
	Juan David Gonzalez Cobas <david.cobas@...il.com>,
	Bill Pemberton <wfp5p@...ginia.edu>
Subject: Re: [PATCH 04/30] staging/vme: allow non-dynamic allocation of bus
 numbers

On Wed, Oct 27, 2010 at 10:41:18 +0100, Martyn Welch wrote:
> On 26/10/10 02:10, Emilio G. Cota wrote:
> > From: Emilio G. Cota <cota@...ap.org>
> > 
> > In a configuration with several bridges, each bridge is
> > assigned a certain bus number depending on the order in which
> > vme_register_bridge is called. This can complicate multi-bridge
> > installations because the eventual bus numbers will depend
> > on the order the bridges were loaded.
> > 
> > The appended allows bridges to register with a bus number of
> > their choice, while keeping the previous 'first come, first
> > served' behaviour as the default.
> > 
> 
> I can't see where this is being used.

Each driver's .probe is fed with bus_number and slot_number.
Normally the driver will check that pair against what it received
through modparams and act accordingly.

For this to be reliable bus numbering should be consistent on
a given system, i.e. it should be possible to always allocate
the same bus number to a given bus. Otherwise, depending on
which bridge is installed first, we'd get different bus numbers
assigned.

Does that make it clearer now?

> I assume this is a part of future changes you wish to make?

AFAICT it affects the current model.

Cheers

		Emilio

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