On 2023-06-01 20:46, Jason Gunthorpe wrote:
On Thu, Jun 01, 2023 at 08:37:45PM +0100, Robin Murphy wrote:
On 2023-05-16 01:00, Jason Gunthorpe wrote:
Robin was able to check the documentation and what fsl_pamu has
historically called detach_dev() is really putting the IOMMU into an
IDENTITY mode.
Unfortunately it was the other way around - it's the call to
fsl_setup_liodns() from fsl_pamu_probe() which leaves everything in bypass
by default (the PAACE_ATM_NO_XLATE part, IIRC), whereas the detach_device()
call here ends up disabling the given device's LIODN altogether
Er, I see.. Let me think about it, you convinced me to change it from
PLATFORM, so maybe we should go back to that if it is all wonky.
FWIW I was thinking more along the lines of a token nominal identity
domain where attach does nothing at all...
There doesn't appear to have ever been any code anywhere for putting
things *back* into bypass after using a VFIO domain, so as-is these
default domains would probably break all DMA :(
Sounds like it just never worked right.
ie going to VFIO mode was always a one way trip and you can't go back
to a kernel driver.
...on the assumption that doing so wouldn't really be any less broken
than it always has been :)
Thanks,
Robin.
I don't think this patch makes it worse because we call the identity
attach_dev in all the same places we called detach_dev in the first
place.
We add an extra call at the start of time, but that call is NOP'd
by this:
if (domain == platform_domain || !domain)
+ return 0;
+
(bah, and the variable name needs updating too)
Honestly, I don't really want to fix FSL since it seems abandoned, so
either this patch or going back to PLATFORM seems like the best option.
Jason
