linux-kernel - Re: IrDA driver fails on PXA255

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Date:	Mon, 30 May 2011 22:01:14 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, 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, 29 May 2011, Russell King - ARM Linux wrote:

> We might as well enable CONFIG_ZONE_DMA for everything if that's what
> you're proposing, because it's not just this driver which will be affected.

I'd certainly suggest at least defaulting it to on for arm if you're going 
to be using GFP_DMA in drivers.

> And as soon as we do that, we completely lose the warnings that stuff
> needs fixing.
> 

That's because nothing needs fixing at that point, the page allocator is 
guaranteed to return lowmem if GFP_DMA is passed and CONFIG_ZONE_DMA is 
enabled, or NULL.  Whether GFP_DMA is correct in the memory allocator is a 
different subject, but those types of audits can easily be done on the 
source code.  In my opinion, we should be doing "select ZONE_DMA" on any 
Kconfig option that builds a driver that unconditionally uses GFP_DMA.

The current behavior exists so that the admin reports the error here so it 
can get fixed up (either by finding that GFP_DMA is unnecessary, selective 
depending on the particular hardware, or modifying the Kconfig) and can 
workaround the problem by forcing CONFIG_ZONE_DMA.
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