linux-kernel - Re: [patch v2] x86: allow ZONE

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Date:	Fri, 15 Apr 2011 13:42:43 +0200
From:	Clemens Ladisch <clemens@...isch.de>
To:	David Rientjes <rientjes@...gle.com>
CC:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch v2] x86: allow ZONE_DMA to be configurable

David Rientjes wrote:
> ZONE_DMA is unnecessary for a large number of machines that do not
> require addressing in the lower 16MB of memory because they do not use
> ISA devices with 16-bit address registers (plus one page byte register).
> 
> This patch allows users to disable ZONE_DMA for x86 if they know they
> will not be using such devices with their kernel.
> ...
>  config ZONE_DMA
> -	def_bool y
> +	bool "DMA memory allocation support" if EXPERT

Better call it "ISA/LPC DMA memory allocation support".

> +	default y

Does it make sense to have this without CONFIG_ISA_DMA_API?

> +	help
> +	  DMA memory allocation support allows old ISA devices with 16-bit
> +	  address registers to allocate memory within the first 16MB of
> +	  address space.  Disable if no such devices will be used.

"Old ISA devices" might be misleading because ISA does not imply actual
ISA slots; please mention LPC devices like the floppy controller and the
parallel port in ECP mode.


Regards,
Clemens
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