Re: [PATCH 2/4] x86/amd_nb: add support for newer PCI topologies

Woods, Brian
2018-11-06T05:55:06Z

On Mon, Nov 05, 2018 at 08:38:40PM +0100, Borislav Petkov wrote:
> On Fri, Nov 02, 2018 at 06:11:07PM +0000, Woods, Brian wrote:
> > Add support for new processors which have multiple PCI root complexes
> > per data fabric/SMN interface.
>
> Please write out abbreviations. I believe it is only you and I who know
> what SMN means. :)

Will do.

> > The interfaces per root complex are redundant and should be skipped.
>
> And I believe it is only you who understands that sentence. :)
>
> Please elaborate why interfaces need to be skipped, *which* interfaces
> need to be skipped and which is the correct interface to access DF/SMN
> through?

See last comment.

> > This makes sure the DF/SMN interfaces get accessed via the correct
> > root complex.
> >
> > Ex:
> > DF/SMN 0 -> 60
> > 40
> > 20
> > 00
> > DF/SMN 1 -> e0
> > c0
> > a0
> > 80
> >
> > Signed-off-by: Brian Woods <brian.woods@amd.com>
> > ---
> > arch/x86/kernel/amd_nb.c | 41 +++++++++++++++++++++++++++++++++++------
> > 1 file changed, 35 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/kernel/amd_nb.c b/arch/x86/kernel/amd_nb.c
> > index 19d489ee2b1e..c0bf26aeb7c3 100644
> > --- a/arch/x86/kernel/amd_nb.c
> > +++ b/arch/x86/kernel/amd_nb.c
> > @@ -213,7 +213,10 @@ int amd_cache_northbridges(void)
> > const struct pci_device_id *root_ids = amd_root_ids;
> > struct pci_dev *root, *misc, *link;
> > struct amd_northbridge *nb;
> > - u16 i = 0;
> > + u16 roots_per_misc = 0;
> > + u16 misc_count = 0;
> > + u16 root_count = 0;
> > + u16 i, j;
> >
> > if (amd_northbridges.num)
> > return 0;
> > @@ -226,26 +229,52 @@ int amd_cache_northbridges(void)
> >
> > misc = NULL;
> > while ((misc = next_northbridge(misc, misc_ids)) != NULL)
> > - i++;
> > + misc_count++;
> >
> > - if (!i)
> > + root = NULL;
> > + while ((root = next_northbridge(root, root_ids)) != NULL)
> > + root_count++;
> > +
> > + if (!misc_count)
> > return -ENODEV;
>
> So you're doing the root_count above but returning in the !misc_count
> case. So that root_count iteration was unnecessary work. IOW, you should
> keep the misc_count check after its loop.

I think having them togeter is cleaner. If you aren't finding any
misc IDs, I highly doubt you'll find any root IDs. There shouldn't
be much of a difference in how fast the function exits, either way.
If you want it the other way though, I don't mind changing it.

> >
> > - nb = kcalloc(i, sizeof(struct amd_northbridge), GFP_KERNEL);
> > + if (root_count) {
> > + roots_per_misc = root_count / misc_count;
> > +
> > + /*
> > + * There should be _exactly_ N roots for each DF/SMN
> > + * interface.
> > + */
> > + if (!roots_per_misc || (root_count % roots_per_misc)) {
> > + pr_info("Unsupported AMD DF/PCI configuration found\n");
> > + return -ENODEV;
> > + }
> > + }
> > +
> > + nb = kcalloc(misc_count, sizeof(struct amd_northbridge), GFP_KERNEL);
> > if (!nb)
> > return -ENOMEM;
> >
> > amd_northbridges.nb = nb;
> > - amd_northbridges.num = i;
> > + amd_northbridges.num = misc_count;
> >
> > link = misc = root = NULL;
> > - for (i = 0; i != amd_northbridges.num; i++) {
> > + for (i = 0; i < amd_northbridges.num; i++) {
> > node_to_amd_nb(i)->root = root =
> > next_northbridge(root, root_ids);
> > node_to_amd_nb(i)->misc = misc =
> > next_northbridge(misc, misc_ids);
> > node_to_amd_nb(i)->link = link =
> > next_northbridge(link, link_ids);
> > +
> > + /*
> > + * If there are more root devices than data fabric/SMN,
> > + * interfaces, then the root devices per DF/SMN
> > + * interface are redundant and N-1 should be skipped so
> > + * they aren't mapped incorrectly.
> > + */
>
> This text is trying to explain it a bit better but you still still need
> to specify which are the redundant ones. All N-1 or is there a special
> root device through which the DF/SMN gets accessed or?
>
> Thx.
Would

/*
* If there are more PCI root devices than data fabric/
* system management network interfaces, then the (N)
* PCI roots per DF/SMN interface are functionally the
* same (for DF/SMN access) and N-1 are redundant. The
* N-1 PCI roots should be skipped per DF/SMN interface
* so the DF/SMN interfaces get mapped to the correct
* PCI root.
*/

be better? I would update the commit msg also.

> --
> Regards/Gruss,
> Boris.
>
> Good mailing practices for 400: avoid top-posting and trim the reply.

--
Brian Woods