linux-kernel - Re: IrDA driver fails on PXA255

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Date:	Sun, 29 May 2011 22:56:56 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Eric Miao <eric.y.miao@...il.com>,
	Samuel Ortiz <samuel@...tiz.org>
Subject: Re: IrDA driver fails on PXA255

On Sun, May 29, 2011 at 02:17:02PM -0700, David Rientjes wrote:
> On Sun, 29 May 2011, Dmitry Eremin-Solenikov wrote:
> 
> > What about changing your patch for less intrusive one (to emit a
> > WARN_ON) for at least one
> > or two major releases and only then changing it back to the current state?
> > 
> 
> That would return memory that is not guaranteed to be within the first 
> 16MB of address space, so a GFP_DMA allocation would succeed with memory 
> not from ZONE_DMA.

Err, no. GFP_DMA returns memory in a zone which the platform has setup.
There's nothing specific about it being "16MB" or any other size; the
arch can chose what size that is.

> That's an invalid configuration, so users, including 
> you, should at least edit their .config by hand to enable CONFIG_ZONE_DMA 
> as a workaround.

Again, no.  This change has caused a load of previously working drivers
to suddenly start failing without _any_ explanation why or even warning
about the change.  It needs to start off as a WARN_ON() so that stuff
can be fixed, and then changed to a hard error.
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