linux-kernel - Enabling RO on a VF

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Message-ID: <48FF6F8E-95E2-4A29-A059-12EF614B381C@oracle.com>
Date:   Fri, 1 Oct 2021 11:05:15 +0000
From:   Haakon Bugge <haakon.bugge@...cle.com>
To:     Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Bjorn Helgaas <bhelgaas@...gle.com>
CC:     OFED mailing list <linux-rdma@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Enabling RO on a VF

Hey,

Commit 1477d44ce47d ("RDMA/mlx5: Enable Relaxed Ordering by default for kernel ULPs") uses pcie_relaxed_ordering_enabled() to check if RO can be enabled. This function checks if the Enable Relaxed Ordering bit in the Device Control register is set. However, on a VF, this bit is RsvdP (Reserved for future RW implementations. Register bits are read-only and must return zero when read. Software must preserve the value read for writes to bits.).

Hence, AFAICT, RO will not be enabled when using a VF.

How can that be fixed?

Thxs, Håkon