On Wed, Jun 12, 2019 at 11:16:03AM +0800, Daniel Drake wrote: > On Wed, Jun 12, 2019 at 3:52 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > Why do you need these to be PCI devices? > > I don't have a particular preference, but was trying to explore the > suggestions from the last round of review: > > https://marc.info/?l=linux-ide&m=147923593001525&w=2 > "implementing a bridge driver like VMD" > http://lists.infradead.org/pipermail/linux-nvme/2017-October/013325.html > "The right way to do this would be to expose a fake PCIe root port > that both the AHCI and NVMe driver bind to." > > > It looks like the main thing > > you get is a hook to bind the driver to. Could you accomplish > > something similar by doing some coordination between the ahci and nvme > > drivers directly, without involving PCI? > > That's basically what Dan Williams originally proposed, and Christoph > Hellwig was not particularly excited by it... > > Can you take a quick at the original patches and see what you think? > https://marc.info/?l=linux-ide&m=147709611121482&w=2 > https://marc.info/?l=linux-ide&m=147709611621483&w=2 > https://marc.info/?l=linux-ide&m=147709612221484&w=2 > https://marc.info/?l=linux-ide&m=147709612721485&w=2 > https://marc.info/?l=linux-ide&m=147709613221487&w=2 I see Christoph's objections starting at https://marc.info/?l=linux-ide&m=147711904724908&w=2 and I agree that this AHCI/NVMe melding is ugly. But given the existence of this ugly hardware, my opinion is that Dan's original patch series (above) is actually a nice way to deal with it. That's exactly the sort of thing I was proposing. Part of Christoph's objection was the issue of how reset works, and that objection absolutely makes sense to me. But IMO adding a fake PCI host bridge and fake PCI devices that really don't work because they have read-only config space just smears the issue over PCI/VFIO/etc in addition to AHCI and NVMe. Bjorn
