Re: [RFC PATCH v2 11/21] PCI: MSI: Add helper function to set system wide MSI support

Sunil V L
2023-10-31T02:00:49Z

On Mon, Oct 30, 2023 at 08:29:13PM +0100, Thomas Gleixner wrote:
> On Mon, Oct 30 2023 at 23:24, Sunil V. L. wrote:
> > On Mon, Oct 30, 2023 at 03:28:53PM +0100, Thomas Gleixner wrote:
> > Just noting related discussion :
> > https://www.spinics.net/lists/linux-serial/msg57616.html
> >
> > The MSI controller on RISC-V (IMSIC) is optional for the platform. So,
> > when by default pci_msi_enable = 1 and the MSI controller is not
> > discovered, we get stack trace like below.
>
> <SNIP>
>
> > So, what I did was, by default call pci_no_msi() to disable MSI and then
> > call pci_set_msi() to enable when MSI controller is probed.
>
> Your taste sensors should have gone out of range ...
>
> > But I think Bjorn's suggestion to depend on PCI_BUS_FLAGS_NO_MSI may be
> > better idea. In that case, we need to set bridge->msi_domain to true in
> > pci_create_root_bus(). Let me know what do you prefer or if I am
> > completely missing something here.
>
> That's definitely more sensible, but as I said in the other thread, Marc
> is the one who did the PCI core/bridge setup magic and he is definitely
> in a better position to answer that bridge->msi_domain question.
>
Thanks!. It looks like Marc introduced bridge->msi_domain in [1] for
exactly the same problem we have with RISC-V + ACPI. Let me remove this
hack and do similar to pci_host_common_probe() in next revision unless I
get objections to that approach.

Sorry, somehow my script didn't copy Marc in the series. Will make sure
I copy him explicitly in next revision.

[1] - https://lore.kernel.org/all/20210330151145.997953-12-maz@kernel.org/

Thanks!
Sunil