Messages in this thread | | | Date | Fri, 15 Apr 2011 13:08:46 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [patch v2] x86: allow ZONE_DMA to be configurable |
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On 04/15/2011 04:42 AM, Clemens Ladisch wrote: > 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. >
This isn't really a very good edit, as ZONE_DMA isn't inherently limited to ISA/LPC devices (and LPC devices which do LPC-native bus mastering DMA are not affected.) ZONE_DMA is used even for some PCI devices which have restrictions on the DMA address mask.
-hpa
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