linux-kernel - Re: Aw: Re: [PATCH] pci: mediatek: fix warning in msi.h

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Message-ID: <87k0v27mve.fsf@nanos.tec.linutronix.de>
Date:   Tue, 03 Nov 2020 11:31:17 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Frank Wunderlich <frank-w@...lic-files.de>,
        Ryder Lee <ryder.lee@...iatek.com>,
        linux-mediatek@...ts.infradead.org,
        Frank Wunderlich <linux@...web.de>,
        linux-kernel@...r.kernel.org,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: Aw: Re: [PATCH] pci: mediatek: fix warning in msi.h

On Tue, Nov 03 2020 at 09:54, Marc Zyngier wrote:
> On 2020-11-02 22:18, Thomas Gleixner wrote:
>> So we really need some other solution and removing the warning is not 
>> an option. If MSI is enabled then we want to get a warning when a PCI
>> device has no MSI domain associated. Explicitly expressing the PCIE
>> brigde misfeature of not supporting MSI is way better than silently
>> returning an error code which is swallowed anyway.
>
> I don't disagree here, though the PCI_MSI_ARCH_FALLBACKS mechanism
> makes it more difficult to establish.

Only for the few leftovers which implement msi_controller, i.e.

drivers/pci/controller/pci-hyperv.c
drivers/pci/controller/pci-tegra.c
drivers/pci/controller/pcie-rcar-host.c
drivers/pci/controller/pcie-xilinx.c

The architectures which select PCI_MSI_ARCH_FALLBACKS are:

arch/ia64/Kconfig:      select PCI_MSI_ARCH_FALLBACKS if PCI_MSI
arch/mips/Kconfig:      select PCI_MSI_ARCH_FALLBACKS if PCI_MSI
arch/powerpc/Kconfig:   select PCI_MSI_ARCH_FALLBACKS           if PCI_MSI
arch/s390/Kconfig:      select PCI_MSI_ARCH_FALLBACKS   if PCI_MSI
arch/sparc/Kconfig:     select PCI_MSI_ARCH_FALLBACKS if PCI_MSI

implement arch_setup_msi_irq() which makes it magically work :)

>> Whatever the preferred way is via flags at host probe time or flagging
>> it post probe I don't care much as long as it is consistent.
>
> Host probe time is going to require some changes in the core PCI api,
> as everything that checks for a MSI domain is based on the pci_bus
> structure, which is only allocated much later.

Yeah, it's nasty. One possible solution is to add flags or a callback to
pci_ops, but it's not pretty either.

I think we should go with the 'mark it after pci_host_probe()' hack for
5.10-rc. The real fix will be larger and go into 5.11.

Thoughts?

Thanks,

        tglx