Re: [RFC PATCH v2 13/21] irqchip: riscv-intc: Add ACPI support for AIA

[Sunil V L]

On Fri, Oct 27, 2023 at 04:59:31PM +0530, Sunil V L wrote:
> Hi Bjorn,
> 
> On Thu, Oct 26, 2023 at 11:51:50AM -0500, Bjorn Helgaas wrote:
> > On Thu, Oct 26, 2023 at 01:53:36AM +0530, Sunil V L wrote:
> > > The RINTC subtype structure in MADT also has information about other
> > > interrupt controllers like MMIO. So, save those information and provide
> > > interfaces to retrieve them when required by corresponding drivers.
> > 
> > > @@ -218,7 +306,19 @@ static int __init riscv_intc_acpi_init(union acpi_subtable_headers *header,
> > 
> > > +	 * MSI controller (IMSIC) in RISC-V is optional. So, unless
> > > +	 * IMSIC is discovered, set system wide MSI support as
> > > +	 * unsupported. Once IMSIC is probed, MSI support will be set.
> > > +	 */
> > > +	pci_no_msi();
> > 
> > It doesn't seem like we should have to tell the PCI core about
> > functionality we *don't* have.
> > 
> > I would think IMSIC would be detected before enumerating PCI devices
> > that might use it, and if we *haven't* found an IMSIC by the time we
> > get to pci_register_host_bridge(), would/should we set
> > PCI_BUS_FLAGS_NO_MSI there?
> >
> The check in pci_register_host_bridge() is like below.
> 
> if (bridge->msi_domain && !dev_get_msi_domain(&bus->dev) &&
>             !pci_host_of_has_msi_map(parent))
>                 bus->bus_flags |= PCI_BUS_FLAGS_NO_MSI;
> 
> When there is no IMSIC, bridge->msi_domain is 0 and hence
> PCI_BUS_FLAGS_NO_MSI will never be set. Do you recommend to set
> PCI_BUS_FLAGS_NO_MSI if bridge->msi_domain is 0? Let me know if I am
> missing something.
> 
What seems to work is, setting bridge->msi_domain = true in
pci_create_root_bus() similar to how pci_host_common_probe() sets for OF
framework. Would that be better solution?

Thanks,
Sunil