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

[Thomas Gleixner]

On Thu, Oct 26 2023 at 11:51, 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?
>
> I see Thomas is cc'd; he'd have better insight.

I was not really involved with this bus and MSI domain logic. Marc
should know. CC'ed.

Thanks,

        tglx