Re: [PATCH v4 3/8] wireless: wl1271: add platform driver to get board data - Russell King

From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: "DebBarma, Tarun Kanti" <tarun.kanti@ti.com>
Cc: "felipe.balbi@nokia.com" <felipe.balbi@nokia.com>,
	Ohad Ben-Cohen <ohad@wizery.com>, Kalle Valo <kalle.valo@iki.fi>,
	"Pandita, Vikram" <vikram.pandita@ti.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"Quadros Roger (Nokia-MS/Helsinki)" <roger.quadros@nokia.com>,
	Tony Lindgren <tony@atomide.com>,
	"linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
	Mark Brown <broonie@opensource.wolfsonmicro.com>,
	"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	Nicolas Pitre <nico@fluxnic.net>, San Mehat <san@google.com>,
	"Chikkature Rajashekar, Madhusudhan" <madhu.cr@ti.com>,
	"Coelho Luciano (Nokia-MS/Helsinki)" <Luciano.Coelho@nokia.com>,
	"linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
	Ido Yariv <ido@wizery.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v4 3/8] wireless: wl1271: add platform driver to get board data
Date: Wed, 11 Aug 2010 22:25:13 +0100	[thread overview]
Message-ID: <20100811212513.GC827@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <5A47E75E594F054BAF48C5E4FC4B92AB0324110AC7@dbde02.ent.ti.com>

On Thu, Aug 12, 2010 at 12:57:18AM +0530, DebBarma, Tarun Kanti wrote:
> 
> > -----Original Message-----
> > From: Felipe Balbi [mailto:felipe.balbi@nokia.com]
> > Sent: Thursday, August 12, 2010 12:27 AM
> > To: DebBarma, Tarun Kanti
> > Cc: Balbi Felipe (Nokia-MS/Helsinki); Ohad Ben-Cohen; linux-
> > wireless@vger.kernel.org; linux-mmc@vger.kernel.org; linux-
> > omap@vger.kernel.org; Ido Yariv; Mark Brown; linux-arm-
> > kernel@lists.infradead.org; Chikkature Rajashekar, Madhusudhan; Coelho
> > Luciano (Nokia-MS/Helsinki); akpm@linux-foundation.org; San Mehat; Quadros
> > Roger (Nokia-MS/Helsinki); Tony Lindgren; Nicolas Pitre; Pandita, Vikram;
> > Kalle Valo
> > Subject: Re: [PATCH v4 3/8] wireless: wl1271: add platform driver to get
> > board data
> > 
> > Hi,
> > 
> > On Wed, Aug 11, 2010 at 08:52:54PM +0200, ext DebBarma, Tarun Kanti wrote:
> > >True; however if we go by that argument than we can also assume pdata
> > >is valid, so that we would not need the below check.
> > 
> > of course not. You can have devices that just play well with default
> > values or devices where you don't need the flexibility of platform data.
> > That's why we check.
> > 
> > platform_device pointers on the other hand, are guaranteed to be always
> > true, if it isn't then you should oops, you deserve to oops because
> > something is really really wrong.
> >
> Sounds perfect!
> What that means is _probe() function makes sense only for cases where we
> have valid platform data because we are returning right at the top if
> pdata is not valid. If this is the case I was curious to know why not
> framework make another check for valid pdata before calling _probe()
> instead of coming all the way to _probe() and then returning! 

Platform devices are not for passing platform data around - they're for
declaring platform hardware devices that we want drivers to handle -
and it depends on the driver whether having platform data is appropriate
or not.

This proposal is, IMHO, abusing the platform device/driver support to
achieve its own goals.  I've outlined a far simpler and easiler solution
which avoids this kind of abuse, and given suggestions on how to extend
it to support multiple instances.