linux-kernel - Re: [PATCH] driver core: simplify platform_get

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Date:	Tue, 28 Jul 2009 09:31:21 -0700
From:	Greg KH <gregkh@...e.de>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Mike Frysinger <vapier@...too.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] driver core: simplify platform_get_resource()

On Tue, Jul 28, 2009 at 11:59:49AM +0100, Mark Brown wrote:
> On Mon, Jul 27, 2009 at 02:20:56PM -0400, Mike Frysinger wrote:
> > The platform_get_resource() function takes a number for the desired index
> > into the resource array, but then does a for loop on the array to get to
> > that index.  Considering the array is linear, the loop overhead is just
> > that -- overhead.  So unless I missed something, convert it into an index
> > check and access the desired resource directly.  Resulting code makes a
> > lot more sense considering its purpose.
> 
> This showed up in linux-next for me today and is causing breakage on at
> least S3C64xx platforms since it changes the resource numbering when
> there's more than one resource type for a device:
> 
> > -	for (i = 0; i < dev->num_resources; i++) {
> > -		struct resource *r = &dev->resource[i];
> > -
> > -		if (type == resource_type(r) && num-- == 0)
> > +	if (num >= 0 && num < dev->num_resources) {
> > +		struct resource *r = &dev->resource[num];
> > +		if (type == resource_type(r))
> 
> Previously the resources were indexed within their type (so you'd get
> I/O resources 0, 1, ..., IRQ resources 0, 1, ... and so on) but now the
> index treats all the resources for a device as a single array, causing
> them to be renumbered for callers.
> 
> This causes drivers doing lookups by number to fail to find their
> resources and not probe, causing widespread breakage.  Reverting the
> patch fixes the problem.

I've now dropped this patch.

thanks,

greg k-h
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