linux-kernel - Re: [PATCH 1/7] spi: Add support for device table matching

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Date:	Thu, 30 Jul 2009 02:40:50 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Ben Dooks <ben-linux@...ff.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	David Woodhouse <dwmw2@...radead.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Jean Delvare <khali@...ux-fr.org>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	lm-sensors@...sensors.org, linuxppc-dev@...abs.org
Subject: Re: [PATCH 1/7] spi: Add support for device table matching

On Thu, Jul 30, 2009 at 02:32:23AM +0400, Anton Vorontsov wrote:
> On Wed, Jul 29, 2009 at 10:44:46PM +0100, Ben Dooks wrote:
> [...]
> > > +	const struct spi_device_id *id_table;
> > > +	int			(*probe_id)(struct spi_device *spi,
> > > +					    const struct spi_device_id *id);
> > 
> > how about leaving it at just probe and have either a call or a field
> > in the device that you can look at to see if this was a new style of
> > call?
> 
> There are no technical difficulties with that, but it would be
> inconsitent wrt other "device table"-aware buses (i2c, pci, of).

Btw, I guess there are few reasons why other buses pass id via
probe() call:

- You'll have to store the "id" in device struct forever, while
  in most cases you only need it during probe(), then you don't
  need it at all;

- If you don't store "id" in the device struct, you'll have
  to look up the device table twice (at first during bus->match(),
  and second time in drivers' probe() hook, i.e.
  probe(struct bus_dev *dev) {
  	id = bus_get_devid(dev); /* here */
  }

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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