Re: [patch v2] x86: allow ZONE_DMA to be configurable

From: Clemens Ladisch
Date: Fri Apr 15 2011 - 07:41:05 EST

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.

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