Re: [PATCH v7 4/4] PCI: Introduce the disable_acs_redir parameter

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 17 Jul 2018 11:02:04 -0600
Logan Gunthorpe <logang@deltatee.com> wrote:

> In order to support P2P traffic on a segment of the PCI hierarchy,
> we must be able to disable the ACS redirect bits for select
> PCI bridges. The bridges must be selected before the devices are
> discovered by the kernel and the IOMMU groups created. Therefore,
> a kernel command line parameter is created to specify devices
> which must have their ACS bits disabled.
> 
> The new parameter takes a list of devices separated by a semicolon.
> Each device specified will have it's ACS redirect bits disabled.
> This is similar to the existing 'resource_alignment' parameter.
> 
> The ACS Request P2P Request Redirect, P2P Completion Redirect and P2P
> Egress Control bits are disabled which is sufficient to always allow
> passing P2P traffic uninterrupted. The bits are set after the kernel
> (optionally) enables the ACS bits itself. It is also done regardless of
> whether the kernel sets the bits or not seeing some BIOS firmware is known
> to set the bits on boot.
> 
> If the user tries to disable the ACS redirct for a device without the
> ACS capability, a warning is printed to dmesg.
> 
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> Reviewed-by: Stephen Bates <sbates@raithlin.com>
> Acked-by: Christian König <christian.koenig@amd.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  9 +++
>  drivers/pci/pci.c                               | 76 ++++++++++++++++++++++++-
>  2 files changed, 83 insertions(+), 2 deletions(-)

Thanks for the re-spins!

Reviewed-by: Alex Williamson <alex.williamson@redhat.com>