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

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Message-ID: <87jzr82c3h.ffs@tglx>
Date:   Fri, 27 Oct 2023 19:45:38 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Sunil V L <sunilvl@...tanamicro.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-acpi@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-serial@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Anup Patel <anup@...infault.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Andrew Jones <ajones@...tanamicro.com>,
        Atish Kumar Patra <atishp@...osinc.com>,
        Haibo Xu <haibo1.xu@...el.com>, Marc Zyngier <maz@...nel.org>
Subject: Re: [RFC PATCH v2 13/21] irqchip: riscv-intc: Add ACPI support for AIA

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