ISA DMA

ISA DMA

[Adrian Cox]

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The current 2.4-devel tree never assigns any memory to the ISA DMA zone,
irrespective of the setting of ISA_DMA_THRESHOLD. As I'm currently
trying to get a floppy working on a platform with 24-bit ISA DMA in its
Southbridge, this looks like a problem.

How do people feel about the attached patch? This should only change
behavior for platforms which set ISA_DMA_THRESHOLD to a value other than
0 or (-1)L.


--
Adrian Cox   http://www.humboldt.co.uk/

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===== arch/ppc/mm/init.c 1.41 vs edited =====
--- 1.41/arch/ppc/mm/init.c	Fri Nov 30 15:07:14 2001
+++ edited/arch/ppc/mm/init.c	Wed Dec 19 10:15:44 2001
@@ -440,11 +440,18 @@
 	kmap_prot = PAGE_KERNEL;
 #endif /* CONFIG_HIGHMEM */

-	/*
-	 * All pages are DMA-able so we put them all in the DMA zone.
-	 */
-	zones_size[ZONE_DMA] = total_lowmem >> PAGE_SHIFT;
-	for (i = 1; i < MAX_NR_ZONES; i++)
+    	if (ISA_DMA_THRESHOLD && ISA_DMA_THRESHOLD < total_lowmem - 1)
+	{
+		zones_size[ZONE_DMA] = (ISA_DMA_THRESHOLD + 1) >> PAGE_SHIFT;
+		zones_size[ZONE_NORMAL] =
+			(total_lowmem - ISA_DMA_THRESHOLD - 1) >> PAGE_SHIFT;
+	}
+	else
+	{
+	    	zones_size[ZONE_DMA] = total_lowmem >> PAGE_SHIFT;
+	    	zones_size[ZONE_NORMAL] = 0;
+	}
+	for (i = 2; i < MAX_NR_ZONES; i++)
 		zones_size[i] = 0;

 #ifdef CONFIG_HIGHMEM

Re: ISA DMA

[David Müller (ELSOFT AG)]

Hi

Seems like you are facing the same problem as i do. But IIRC i think you
have to adjust the code in include/asm/dma.h (and possibly other places)
as well (at least in 2.4.14, not sure about the later kernels).

BTW:

What south bridge do you use? Some of the newer ones offer 32bit
addressing capability for DMA.

Adrian Cox wrote:

> The current 2.4-devel tree never assigns any memory to the ISA DMA zone,
> irrespective of the setting of ISA_DMA_THRESHOLD. As I'm currently
> trying to get a floppy working on a platform with 24-bit ISA DMA in its
> Southbridge, this looks like a problem.
>
> How do people feel about the attached patch? This should only change
> behavior for platforms which set ISA_DMA_THRESHOLD to a value other than
> 0 or (-1)L.
>


[stuff deleted]


Dave


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Re: ISA DMA

[Adrian Cox]

David Müller (ELSOFT AG) wrote:


> Seems like you are facing the same problem as i do. But IIRC i think you
> have to adjust the code in include/asm/dma.h (and possibly other places)
> as well (at least in 2.4.14, not sure about the later kernels).


The main problem I can see is that the code always writes to the
DMA_HI_PAGE_x registers, irrespective of whether they actually exist.
This should be harmless, as nothing else is mapped to those locations.


> What south bridge do you use? Some of the newer ones offer 32bit
> addressing capability for DMA.


Via686a. As I understand it, 32-bit DMA uses the DMA_HI_PAGE_x registers
from 0x487 to 0x48a, and the Via manual doesn't claim to have any
registers in that range. The only 32-bit DMA southbridge I've
encountered is the Winbond chip on the Sandpoint, and that chip doesn't
have UDMA66, USB, and audio.


--
Adrian Cox   http://www.humboldt.co.uk/


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Re: ISA DMA

[Geert Uytterhoeven]

On Thu, 20 Dec 2001, Adrian Cox wrote:
> David Müller (ELSOFT AG) wrote:
> > What south bridge do you use? Some of the newer ones offer 32bit
> > addressing capability for DMA.
>
> Via686a. As I understand it, 32-bit DMA uses the DMA_HI_PAGE_x registers
> from 0x487 to 0x48a, and the Via manual doesn't claim to have any
> registers in that range. The only 32-bit DMA southbridge I've
> encountered is the Winbond chip on the Sandpoint, and that chip doesn't
> have UDMA66, USB, and audio.

And the Winbond South Bridge on the LongTrail (most probably the same chip).

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


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Re: ISA DMA

[Michael Sokolov]

Adrian Cox <adrian@humboldt.co.uk> wrote:

> Via686a. As I understand it, 32-bit DMA uses the DMA_HI_PAGE_x registers
> from 0x487 to 0x48a, and the Via manual doesn't claim to have any
> registers in that range.

It is also my understanding that VT82C686/A/B offers 24-bit DMA addressing
only.

On the Adirondack I plan to use the floppy disk controller (the only ISA DMA
user) in non-DMA mode only. I hope Linux can do that. The memory map we've
adopted does not have memory at PCI address 0 at all, so 24-bit DMA means no
DMA at all rather than bottom 16 MB only. It is really too late to change the
memory map now, it would be so much pain that I would much rather settle for
using non-DMA mode only for floppies.

> The only 32-bit DMA southbridge I've
> encountered is the Winbond chip on the Sandpoint, and that chip doesn't
> have UDMA66, USB, and audio.

Acer Labs 1543 has it according to its manual (see the latter for where the
registers are, I don't remember).

We have that bridge on the K2. Ironically, there we don't have a floppy disk
port, so we have good ISA DMA on the board where we don't need it but don't
have it on a board where we do...

MS

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