ZONE_DMA on MIPS

ZONE_DMA on MIPS

[Atsushi Nemoto]

Some ZONE_DMA patches were merged in 2.6.21.  On most MIPS, ZONE_DMA
is not needed, isn't it?

Currently JAZZ, MALTA, QEMU, IP22, SNI_RM, RBTX4938 defines
GENERIC_ISA_DMA so they may need ZONE_DMA (though I wonder QEMU or
RBTX4938 really need it...)

Are there any other platforms requires special DMA zone?

---
Atsushi Nemoto

Re: ZONE_DMA on MIPS

[Sergei Shtylyov]

Hello.

Atsushi Nemoto wrote:
> Some ZONE_DMA patches were merged in 2.6.21.  On most MIPS, ZONE_DMA
> is not needed, isn't it?
> 
> Currently JAZZ, MALTA, QEMU, IP22, SNI_RM, RBTX4938 defines
> GENERIC_ISA_DMA so they may need ZONE_DMA (though I wonder QEMU or
> RBTX4938 really need it...)

    Erm, concertning the latter -- probably not, as I'm not seeing other 
FPCIB0 backplane support in the source.

> Are there any other platforms requires special DMA zone?

    Erm, RBHMA4[24]00 have 8259 on the backplane... And the NEC boards with 
the Rockhopper backplane as well...

> ---
> Atsushi Nemoto

WBR, Sergei

Re: ZONE_DMA on MIPS

[Atsushi Nemoto]

On Mon, 19 Mar 2007 18:32:33 +0300, Sergei Shtylyov <sshtylyov@ru.mvista.com> wrote:
> > Are there any other platforms requires special DMA zone?
> 
>     Erm, RBHMA4[24]00 have 8259 on the backplane... And the NEC boards with 
> the Rockhopper backplane as well...

Having 8259 does not mean it uses ISA DMA.  IIRC FPCIB0 backplane does
not have real ISA slot, and no on-board device uses ISA DMA.  Does
Rockhopper backplace have ISA slot?

---
Atsushi Nemoto

Re: ZONE_DMA on MIPS

[Sergei Shtylyov]

Hello.

Atsushi Nemoto wrote:

>>>Are there any other platforms requires special DMA zone?

>>    Erm, RBHMA4[24]00 have 8259 on the backplane... And the NEC boards with 
>>the Rockhopper backplane as well...

> Having 8259 does not mean it uses ISA DMA.  IIRC FPCIB0 backplane does
> not have real ISA slot, and no on-board device uses ISA DMA.

    No, it does have ISA slot (a single one)! :-D

> Does Rockhopper backplace have ISA slot?

    No, that one doesn't. :-)

> ---
> Atsushi Nemoto

WBR, Sergei

Re: ZONE_DMA on MIPS

[Ralf Baechle]

On Tue, Mar 20, 2007 at 12:09:47AM +0900, Atsushi Nemoto wrote:

> Some ZONE_DMA patches were merged in 2.6.21.  On most MIPS, ZONE_DMA
> is not needed, isn't it?
> 
> Currently JAZZ, MALTA, QEMU, IP22, SNI_RM, RBTX4938 defines
> GENERIC_ISA_DMA so they may need ZONE_DMA (though I wonder QEMU or
> RBTX4938 really need it...)
> 
> Are there any other platforms requires special DMA zone?

Qemu supports more or less the full PC braind^Wheritage, including the
good old too-old floppy controller.  IP22 supports Indigo 2 systems
which have EISA support, so we only want ZONE_DMA if EISA is enabled.
For a bunch of other systems ZONE_DMA may be required to support b0rked
PCI cards that only support like 31-bit DMA addresses or even less.

  Ralf

Re: ZONE_DMA on MIPS

[Atsushi Nemoto]

On Mon, 19 Mar 2007 15:48:21 +0000, Ralf Baechle <ralf@linux-mips.org> wrote:
> > Are there any other platforms requires special DMA zone?
> 
> Qemu supports more or less the full PC braind^Wheritage, including the
> good old too-old floppy controller.  IP22 supports Indigo 2 systems
> which have EISA support, so we only want ZONE_DMA if EISA is enabled.
> For a bunch of other systems ZONE_DMA may be required to support b0rked
> PCI cards that only support like 31-bit DMA addresses or even less.

Hmm... So do you think making ZONE_DMA customizable for each platform
(or user configurable) would have some sense?

For these legacy(?) PCI cards, we can check if it works or not by
pci_set_dma_mask(), at least.

---
Atsushi Nemoto

Re: ZONE_DMA on MIPS

[Ralf Baechle]

On Tue, Mar 20, 2007 at 01:36:08AM +0900, Atsushi Nemoto wrote:

> On Mon, 19 Mar 2007 15:48:21 +0000, Ralf Baechle <ralf@linux-mips.org> wrote:
> > > Are there any other platforms requires special DMA zone?
> > 
> > Qemu supports more or less the full PC braind^Wheritage, including the
> > good old too-old floppy controller.  IP22 supports Indigo 2 systems
> > which have EISA support, so we only want ZONE_DMA if EISA is enabled.
> > For a bunch of other systems ZONE_DMA may be required to support b0rked
> > PCI cards that only support like 31-bit DMA addresses or even less.
> 
> Hmm... So do you think making ZONE_DMA customizable for each platform
> (or user configurable) would have some sense?

It's probably reasonable to do something like:

config GENERIC_ISA_DMA
	bool
	select ZONE_DMA

I don't think we should expose such deep technical details to the Kconfig
user.

> For these legacy(?) PCI cards, we can check if it works or not by
> pci_set_dma_mask(), at least.

The Linux approach to handling such broken cards is not very gentle.  A
card that can't live with normal allocations, will always use bounce
ZONE_NORMAL buffers.

Obviously the message to the designers of PCI cards is to get their stuff
done right and not rely on OS kludgery to fix hardware shortcomings.

And while at it, we may want to think about ZONE_DMA32.  At least the
BCM1250 needs it for configs with more than 1GB memory due to it's
sparse memory map.

  Ralf

Re: ZONE_DMA on MIPS

[Atsushi Nemoto]

On Mon, 19 Mar 2007 22:20:31 +0000, Ralf Baechle <ralf@linux-mips.org> wrote:
> It's probably reasonable to do something like:
> 
> config GENERIC_ISA_DMA
> 	bool
> 	select ZONE_DMA
> 
> I don't think we should expose such deep technical details to the Kconfig
> user.

Thanks.  I'll try.  GENERIC_ISA_DMA_SUPPORT_BROKEN also should select
ZONE_DMA, right?

---
Atsushi Nemoto

Re: ZONE_DMA on MIPS

[Ralf Baechle]

On Tue, Mar 20, 2007 at 11:10:13PM +0900, Atsushi Nemoto wrote:

> On Mon, 19 Mar 2007 22:20:31 +0000, Ralf Baechle <ralf@linux-mips.org> wrote:
> > It's probably reasonable to do something like:
> > 
> > config GENERIC_ISA_DMA
> > 	bool
> > 	select ZONE_DMA
> > 
> > I don't think we should expose such deep technical details to the Kconfig
> > user.
> 
> Thanks.  I'll try.  GENERIC_ISA_DMA_SUPPORT_BROKEN also should select
> ZONE_DMA, right?

That one is actually a more interesting issue.  GENERIC_ISA_DMA_SUPPORT_BROKEN
is needed on Indigo 2 but Indigo 2 has no mmeory other than a little bit
for the exception vectors mapped into the low 16MB.  At this stage nobody
seems to know if the machine actually can support ISA DMA or not.
Anyway, that means that for now it seems better to leave ZONE_DMA
disabled.

But maybe somebody who knows a little more about EISA support on Indigo 2
should comment.

  Ralf