> -----Original Message-----
> From: Burakov, Anatoly <anatoly.bura...@intel.com>
> Sent: Tuesday, July 23, 2019 7:27 PM
> To: Thomas Monjalon <tho...@monjalon.net>
> Cc: Jerin Jacob Kollanukkaran <jer...@marvell.com>; Stojaczyk, Dariusz
> <dariusz.stojac...@intel.com>; David Marchand
> <david.march...@redhat.com>; dev@dpdk.org
> Subject: [EXT] Re: [dpdk-dev] [PATCH v4 0/4] Fixes on IOVA mode selection
>
> ----------------------------------------------------------------------
> On 23-Jul-19 11:25 AM, Thomas Monjalon wrote:
> > 23/07/2019 11:57, Burakov, Anatoly:
> >> A machine without an IOMMU shouldn't have picked IOVA as VA in the
> >> first place. Perhaps this is something we could fix? I'm not sure how
> >> to detected that condition though, i don't think there's a mechanism
> >> to know that for sure. Some kernels create a "iommu" sysfs
> >> directories, but i'm not too sure if they're 1) there for older
> >> kernels we support, and
> >> 2) always there.
> > [..]
> >> On my machine, "/sys/devices/virtual/iommu" exists when IOMMU is
> >> enabled, but doesn't exist if it isn't ("/sys/class/iommu" exists in
> >> both cases, but is empty when IOMMU is disabled). Perhaps we could go
> >> off that?
> >
> > Yes, good idea.
> > We need to check how these sysfs entries are managed, and how old they
> > are by looking at Linux code history.
> >
>
> Quick (and by no means thorough) Google reveals that IOMMU driver's
> sysfs-related code dates back as far as kernel version 3.17:
>
> https://elixir.bootlin.com/linux/v3.17.8/source/drivers/iommu/iommu-
> sysfs.c
>
> I'm not a kernel code expert, but the code *looks* like it's creating an
> IOMMU-related entry in sysfs. So, i take it we can be reasonably sure of
> these entries' presence at least since v3.17 onwards? Do we support kernels
> which don't have this code?
I checked with a x86 and arm64 machine. I could not see
"/sys/devices/virtual/iommu"
But looks like "/sys/class/iommu/" present when iommu present.
$ uname -a
Linux jerin-lab 5.1.15-arch1-1-ARCH #1 SMP PREEMPT Tue Jun 25 04:49:39 UTC 2019
x86_64 GNU/Linux
$ ls /sys/devices/virtual/
bdi dmi drm graphics mem misc msr net powercap thermal tty vc
vtconsole workqueue
# ls /sys/class/iommu/
# uname -a
Linux alarm 4.14.76-5.0.0-g12f0519 #63 SMP PREEMPT Thu Jul 11 17:43:54 IST 2019
aarch64 GNU/Linux
# ls /sys/devices/virtual/
bdi block graphics input mem misc net otx-bphy-ctr otx-gpio-ctr ppp
tty vc vfio vtconsole workqueue
# ls /sys/class/iommu/
smmu3.0x0000830000000000
>
> --
> Thanks,
> Anatoly
