On Thu, Jul 23, 2020 at 4:11 PM Logan Gunthorpe <[email protected]> wrote: > > > > On 2020-07-23 1:57 p.m., Bjorn Helgaas wrote: > > [+cc Andrew, Armen, hpa] > > > > On Thu, Jul 23, 2020 at 02:01:17PM -0400, Alex Deucher wrote: > >> On Thu, Jul 23, 2020 at 1:43 PM Logan Gunthorpe <[email protected]> > >> wrote: > >>> > >>> The AMD Zen 2 root complex (Starship/Matisse) was tested for P2PDMA > >>> transactions between root ports and found to work. Therefore add it > >>> to the list. > >>> > >>> Signed-off-by: Logan Gunthorpe <[email protected]> > >>> Cc: Bjorn Helgaas <[email protected]> > >>> Cc: Christian König <[email protected]> > >>> Cc: Huang Rui <[email protected]> > >>> Cc: Alex Deucher <[email protected]> > >> > >> Starting with Zen, all AMD platforms support P2P for reads and writes. > > > > What's the plan for getting out of the cycle of "update this list for > > every new chip"? Any new _DSMs planned, for instance? > > Well there was an effort to add capabilities in the PCI spec to describe > this but, as far as I know, they never got anywhere, and hardware still > doesn't self describe with this. > > > A continuous trickle of updates like this is not really appealing. So > > far we have: > > > > 7d5b10fcb81e ("PCI/P2PDMA: Add AMD Zen Raven and Renoir Root Ports to > > whitelist") > > 7b94b53db34f ("PCI/P2PDMA: Add Intel Sky Lake-E Root Ports B, C, D to the > > whitelist") > > bc123a515cb7 ("PCI/P2PDMA: Add Intel SkyLake-E to the whitelist") > > 494d63b0d5d0 ("PCI/P2PDMA: Whitelist some Intel host bridges") > > 0f97da831026 ("PCI/P2PDMA: Allow P2P DMA between any devices under AMD > > ZEN Root Complex") > > > > And that's just from the last year, not including this patch. > > Yes, it's not ideal. But most of these are adding old devices as people > test and care about running on those platforms -- a lot of this is > bootstrapping the list. I'd expect this to slow down a bit as by now we > have hopefully got a lot of the existing platforms people care about. > But we'd still probably expect to be adding a new Intel and AMD devices > about once a year as they produce new hardware designs. > > Unless, the Intel and AMD folks know of a way to detect this, or even to > query if a root complex is newer than a certain generation, I'm not sure > what else we can do here.
I started a thread internally to see if I can find a way. FWIW, pre-ZEN parts also support p2p DMA, but only for writes. If I can get a definitive list, maybe we could switch to a blacklist for the old ones? Alex > > Logan
