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

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Date:   Fri, 27 Oct 2023 17:24:51 +0530
From:   Sunil V L <sunilvl@...tanamicro.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
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>,
        Thomas Gleixner <tglx@...utronix.de>,
        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>
Subject: Re: [RFC PATCH v2 13/21] irqchip: riscv-intc: Add ACPI support for
 AIA

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