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

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

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>

-- 
Thanks,
Anatoly