* Again ISA DMA question
@ 2005-03-28 19:08 Pavel Fedin
2005-03-28 10:16 ` Gabriel Paubert
2005-03-28 11:07 ` Benjamin Herrenschmidt
0 siblings, 2 replies; 3+ messages in thread
From: Pavel Fedin @ 2005-03-28 19:08 UTC (permalink / raw)
To: linuxppc-dev
Hello, all!
In a source code or AROS operating system (http://www.aros.org) i
found this comment:
--- cut ---
The older PReP machines have the DMA area limited to first 16MB of
system
memory. Therefore it is reasonable, to place the kernel at the end
of DMA
RAM. Both areas may be then easily separated.
--- cut ---
Does this mean that Linux has an option to limit DMA memory space to
first 16 MB? PReP machines are fully supported i guess. Or not fully?
Kind regards
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: Again ISA DMA question
2005-03-28 19:08 Again ISA DMA question Pavel Fedin
@ 2005-03-28 10:16 ` Gabriel Paubert
2005-03-28 11:07 ` Benjamin Herrenschmidt
1 sibling, 0 replies; 3+ messages in thread
From: Gabriel Paubert @ 2005-03-28 10:16 UTC (permalink / raw)
To: Pavel Fedin; +Cc: linuxppc-dev
On Mon, Mar 28, 2005 at 02:08:38PM -0500, Pavel Fedin wrote:
> Hello, all!
>
> In a source code or AROS operating system (http://www.aros.org) i
> found this comment:
>
> --- cut ---
> The older PReP machines have the DMA area limited to first 16MB of
> system
> memory. Therefore it is reasonable, to place the kernel at the end
> of DMA
> RAM. Both areas may be then easily separated.
> --- cut ---
>
> Does this mean that Linux has an option to limit DMA memory space to
> first 16 MB? PReP machines are fully supported i guess. Or not fully?
Well, actually if you are courageous, many PreP machines have an
extended ISA DMA with 32 bits addressing capability (this depends
on the ISA bridge). But ISA DMA is only used for floppy and I have
never connected a floppy to my Prep machines sicne I got the first
one back in 1997.
Regards,
Gabriel
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Again ISA DMA question
2005-03-28 19:08 Again ISA DMA question Pavel Fedin
2005-03-28 10:16 ` Gabriel Paubert
@ 2005-03-28 11:07 ` Benjamin Herrenschmidt
1 sibling, 0 replies; 3+ messages in thread
From: Benjamin Herrenschmidt @ 2005-03-28 11:07 UTC (permalink / raw)
To: Pavel Fedin; +Cc: linuxppc-dev list
On Mon, 2005-03-28 at 14:08 -0500, Pavel Fedin wrote:
> Hello, all!
>
> In a source code or AROS operating system (http://www.aros.org) i
> found this comment:
>
> --- cut ---
> The older PReP machines have the DMA area limited to first 16MB of
> system
> memory. Therefore it is reasonable, to place the kernel at the end
> of DMA
> RAM. Both areas may be then easily separated.
> --- cut ---
>
> Does this mean that Linux has an option to limit DMA memory space to
> first 16 MB? PReP machines are fully supported i guess. Or not fully?
Linux can do it, but we choose no to implement this on ppc, as slicing
the memory into zones has disadvantages. Only legacy ISA DMA is
concerned, which is mostly not a problem. PCI DMA shouldn't be limited.
Ben.
^ permalink raw reply [flat|nested] 3+ messages in thread
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