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

[Bjorn Helgaas]

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.

Bjorn