linux-kernel - Re: [RFC PATCH v2 11/21] PCI: MSI: Add helper function to set system wide MSI support

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Message-ID: <ZUBfw2vrzc+GyAny@sunil-laptop>
Date:   Tue, 31 Oct 2023 07:30:35 +0530
From:   Sunil V L <sunilvl@...tanamicro.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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 11/21] PCI: MSI: Add helper function to set system
 wide MSI support

On Mon, Oct 30, 2023 at 08:29:13PM +0100, Thomas Gleixner wrote:
> On Mon, Oct 30 2023 at 23:24, Sunil V. L. wrote:
> > On Mon, Oct 30, 2023 at 03:28:53PM +0100, Thomas Gleixner wrote:
> > Just noting related discussion :
> > https://www.spinics.net/lists/linux-serial/msg57616.html
> >
> > The MSI controller on RISC-V (IMSIC) is optional for the platform. So,
> > when by default pci_msi_enable = 1 and the MSI controller is not
> > discovered, we get stack trace like below.
> 
> <SNIP>
> 
> > So, what I did was, by default call pci_no_msi() to disable MSI and then
> > call pci_set_msi() to enable when MSI controller is probed.
> 
> Your taste sensors should have gone out of range ...
> 
> > But I think Bjorn's suggestion to depend on PCI_BUS_FLAGS_NO_MSI may be
> > better idea. In that case, we need to set bridge->msi_domain to true in
> > pci_create_root_bus(). Let me know what do you prefer or if I am
> > completely missing something here.
> 
> That's definitely more sensible, but as I said in the other thread, Marc
> is the one who did the PCI core/bridge setup magic and he is definitely
> in a better position to answer that bridge->msi_domain question.
> 
Thanks!. It looks like Marc introduced bridge->msi_domain in [1] for
exactly the same problem we have with RISC-V + ACPI. Let me remove this
hack and do similar to pci_host_common_probe() in next revision unless I
get objections to that approach.

Sorry, somehow my script didn't copy Marc in the series. Will make sure
I copy him explicitly in next revision.

[1] - https://lore.kernel.org/all/20210330151145.997953-12-maz@kernel.org/

Thanks!
Sunil