Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [patch 21/32] NTB/msi: Convert to msi_on_each_desc() | Date | Wed, 01 Dec 2021 15:52:02 +0100 |
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On Tue, Nov 30 2021 at 22:23, Thomas Gleixner wrote: > On Tue, Nov 30 2021 at 16:28, Jason Gunthorpe wrote: > > The real problem is where to store the MSI descriptors because the PCI > device has its own real PCI/MSI-X interrupts which means it still shares > the storage space.
Bah. I confused myself by staring at the existing code instead of looking at how this NTB stuff actually works.
So if I understand it correctly then the end result looks like this:
1) PCIe device (switchtec)
The device has 4 MSI[X] interrupts: event, dma_rpc, message, doorbell. The event and dma_rpc interrupts are requested by the switchtec PCI driver itself.
2) Switchtec character device
The switchtec PCI driver creates a character device which is exposed for device specific IOCTLs
The device belongs to the switchtec_class device class.
3) Switchtec NTB device
The ntb_hw_switchtec driver registers the switchtec_class class interface.
So when #2 is registered with the driver core the switchtec class interface add_dev() function is invoked. That function creates a NTB device, requests the message and the doorbell interrupts which have been allocated by the underlying PCIe device driver (#1) and registers the NTB device with the NTB core.
4) The NTB core then tries to use the virtual MSI vectors which have been allocated by the switchtec driver in #1 and requires the msg write intercept to actually expose it to the peers.
So we really can go and create a MSI irqdomain and stick the pointer into stdev->dev.irqdomain. The parent domain of this irqdomain is
stdev->pdev.dev.irqdomain->parent
which is either the irq remapping domain or the vector domain. Which is pretty much what I proposed as general facility for IMS/IDXD. I need to go back and polish that up on top of the current pile.
Along with that have an irq chip implementation which exposes:
static struct irq_chip ntb_chip = { .name = "ntb", .irq_ack = irq_chip_ack_parent, .irq_write_msi_msg = ntb_msi_write_msg, #ifdef CONFIG_SMP .irq_set_affinity = irq_chip_set_affinity_parent, #endif };
We just need some reasonable solution for the DMA/remap problem Jason mentioned vs. msi_desc::dev, but that wants to be cleaned up in any case for all the aliasing muck.
Thanks,
tglx
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