Re: [dpdk-dev] [PATCH] eal: forcing IOVA as PA in ppc

[David Marchand <david.marchand@redhat.com>]

Hello Anatoly,

On Wed, Jul 31, 2019 at 5:36 AM Takeshi Yoshimura <tyos@jp.ibm.com> wrote:
>
> Commit b76fafb174d2 ("eal: fix IOVA mode selection as VA for PCI
> drivers") breaks ppc apps with no IOVA configs (or RTE_IOVA_DC)
> because of the inconsistency of user's request and the result of
> device capability for IOVA mode. I updated the code to force IOVA as
> PA in ppc as before because current ppc driver does not support VA
> mode.
>
> Theoretically, ppc can support VA mode, but I suspect that ppc with
> VA mode may have performance issues to create a big DMA window
> (VA often uses higher addresses than PA). So, I didn't change the
> code to check device capability in ppc.
>
> Signed-off-by: Takeshi Yoshimura <tyos@jp.ibm.com>
> ---
>  lib/librte_eal/linux/eal/eal.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/lib/librte_eal/linux/eal/eal.c b/lib/librte_eal/linux/eal/eal.c
> index 946222ccd..db2dec922 100644
> --- a/lib/librte_eal/linux/eal/eal.c
> +++ b/lib/librte_eal/linux/eal/eal.c
> @@ -1121,6 +1121,12 @@ rte_eal_init(int argc, char **argv)
>                                 RTE_LOG(DEBUG, EAL, "KNI can not work since physical addresses are unavailable\n");
>                         }
>                 }
> +#endif
> +#ifdef RTE_ARCH_PPC_64
> +               if (iova_mode == RTE_IOVA_VA) {
> +                       iova_mode = RTE_IOVA_PA;
> +                       RTE_LOG(WARNING, EAL, "Forcing IOVA as 'PA' because PPC uses PA mode.\n");
> +               }
>  #endif
>                 rte_eal_get_configuration()->iova_mode = iova_mode;
>         } else {
> --
> 2.17.1
>

Afaiu, this problem is linked to a specific iommu implementation.
Does it make sense to introduce a check "iommu_support_va" in eal, a
bit like what we have in the pci bus ?


-- 
David Marchand