Re: [dpdk-dev] [PATCH] raw/ioat: fix bus requiring virtual addressing when no devs

["Van Haaren, Harry" <harry.van.haaren@intel.com>]

> -----Original Message-----
> From: Burakov, Anatoly <anatoly.burakov@intel.com>
> Sent: Thursday, May 6, 2021 4:17 PM
> To: Richardson, Bruce <bruce.richardson@intel.com>; dev@dpdk.org
> Cc: Van Haaren, Harry <harry.van.haaren@intel.com>
> Subject: Re: [PATCH] raw/ioat: fix bus requiring virtual addressing when no devs
> 
> On 06-May-21 4:09 PM, Bruce Richardson wrote:
> > If after a bus scan, there are no devices using a particular bus, then
> > that bus should not be taken into account when deciding whether DPDK
> > should be run in VA or PA addressing mode. This becomes an issue when
> > the DSA bus driver code is used on a system without an IOMMU. The PCI
> > bus correctly reports that it only works in PA mode, while the DSA bus -
> > also correctly - reports that it works only in VA mode. The difference
> > is that there will be no devices found in a scan for the DSA bus, since
> > the kernel driver can only present those to userspace in the presence of
> > an IOMMU.
> >
> > While we could change DSA instance to always report that it does not
> > care about the addressing mode, this would imply that it could be used
> > with DPDK in PA mode which is not the case. Therefore, this patch
> > changes the driver to report DC (don't care) in the case where no
> > devices are present, and VA otherwise.
> >
> > NOTE: this addressing mode use of VA-only applies only in the case of
> > using DSA through the idxd kernel driver. The use of DSA though vfio-pci
> > is unaffected and works as with other PCI devices.
> >
> > Fixes: b7aaf417f936 ("raw/ioat: add bus driver for device scanning automatically")
> >
> > Reported-by: Harry van Haaren <harry.van.haaren@intel.com>
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > ---
> 
> Tested-by: Anatoly Burakov <anatoly.burakov@intel.com>

Tested-by: Harry van Haaren <harry.van.haaren@intel.com>