Re: [OpenBIOS] [PATCH] Fix up LANCE ethernet DMA mapping under Solaris 8 on SPARC32.

[Blue Swirl]

      On Mon, Apr 25, 2011 at 7:48 PM, Mark Cave-Ayland
<mark.cave-ayland(a)siriusit.co.uk&gt; wrote:
  It seems that Solaris doesn't set up a DMA mapping
for the LANCE DMA buffers
 and hence must inherit this from OpenBIOS. To make things more complicated,
 Solaris appears to assume that the buffers are fixed at 0xff000000 rather
 than detecting this information from the OpenBIOS IOMMU pagetable before
 switching. Mimicking this behaviour with a fixed location allows Solaris
 8 to correctly use the network card under QEMU.

 Signed-off-by: Mark Cave-Ayland <mark.cave-ayland(a)siriusit.co.uk&gt;
Would it make any difference if IOMMU region were 16M so that the base
would start at 0xff000000?

Otherwise the patch looks OK.

[PATCH] Fix up LANCE ethernet DMA mapping under Solaris 8 on SPARC32.

[Mark Cave-Ayland]

      On 25/04/11 19:11, Blue Swirl wrote:

  Would it make any difference if IOMMU region were 16M
so that the base
 would start at 0xff000000?

 Otherwise the patch looks OK.
Maybe, but there are still difficulties with that. For example, ESP 
claims its IOMMU memory first, so I was seeing that ESP would get 
0xfe000000 while LANCE would get 0xfe001000 - so even changing the base 
is no guarantee this will work. And of course, as soon as the kernel 
takes over the IOMMU page table then the existing mappings disappear - 
unless there is some weird kernel logic that only preserves mappings 
above a certain limit such as 0xff000000?

So in short, given the amount of effort involved for a similar result I 
don't see many advantages over the fixed address mapping implemented in 
the patch.


ATB,

Mark.

-- 
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
http://www.siriusit.co.uk
t: [phone]

Sirius Labs: http://www.siriusit.co.uk/labs

[PATCH] Fix up LANCE ethernet DMA mapping under Solaris 8 on SPARC32.

[Blue Swirl]

      On Mon, Apr 25, 2011 at 10:05 PM, Mark Cave-Ayland
<mark.cave-ayland(a)siriusit.co.uk&gt; wrote:
  On 25/04/11 19:11, Blue Swirl wrote:

  Would it make any difference if IOMMU region were
16M so that the base
 would start at 0xff000000?

 Otherwise the patch looks OK.
 Maybe, but there are still difficulties with that. For example, ESP claims
 its IOMMU memory first, so I was seeing that ESP would get 0xfe000000 while
 LANCE would get 0xfe001000 - so even changing the base is no guarantee this
 will work. And of course, as soon as the kernel takes over the IOMMU page
 table then the existing mappings disappear - unless there is some weird
 kernel logic that only preserves mappings above a certain limit such as
 0xff000000?

 So in short, given the amount of effort involved for a similar result I
 don't see many advantages over the fixed address mapping implemented in the
 patch.
It's fine then. It's just good to know that this is a bit of a hack.

[PATCH] Fix up LANCE ethernet DMA mapping under Solaris 8 on SPARC32.

[Mark Cave-Ayland]

      On 25/04/11 21:51, Blue Swirl wrote:

  So in short,
given the amount of effort involved for a similar result I
 don't see many advantages over the fixed address mapping implemented in the
 patch.
 It's fine then. It's just good to know that this is a bit of a hack.
That's what it feels like, although I would say it's a workaround for a 
Solaris kernel bug. Hopefully the commit message and the comment are 
verbose enough so that if/when someone does work out what the right 
behaviour should be, they can change it with a reasonable degree of 
confidence.

Are you happy for me to commit this, with just a minor change to add the 
CONFIG_DEBUG_SBUS variable into sparc32_config.xml?


ATB,

Mark.

-- 
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
http://www.siriusit.co.uk
t: [phone]

Sirius Labs: http://www.siriusit.co.uk/labs

[PATCH] Fix up LANCE ethernet DMA mapping under Solaris 8 on SPARC32.

[Blue Swirl]

      On Tue, Apr 26, 2011 at 12:59 AM, Mark Cave-Ayland
<mark.cave-ayland(a)siriusit.co.uk&gt; wrote:
  On 25/04/11 21:51, Blue Swirl wrote:

  So in
short, given the amount of effort involved for a similar result I
 don't see many advantages over the fixed address mapping implemented in
 the
 patch.
 It's fine then. It's just good to know that this is a bit of a hack.
 That's what it feels like, although I would say it's a workaround for a
 Solaris kernel bug. Hopefully the commit message and the comment are verbose
 enough so that if/when someone does work out what the right behaviour should
 be, they can change it with a reasonable degree of confidence.

 Are you happy for me to commit this, with just a minor change to add the
 CONFIG_DEBUG_SBUS variable into sparc32_config.xml?
Yes, it's OK.

Maybe we should also have tracepoints like QEMU or Linux kernel.
Something that can be enabled at run time.