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

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Date:   Tue, 03 Nov 2020 11:16:56 +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:
>> On Mon, Nov 02 2020 at 17:16, Thomas Gleixner wrote:
>>> On Mon, Nov 02 2020 at 11:30, Marc Zyngier wrote:
>>>> --- a/drivers/pci/probe.c
>>>> +++ b/drivers/pci/probe.c
>>>> @@ -871,6 +871,8 @@ static void pci_set_bus_msi_domain(struct pci_bus
>>>> *bus)
>>>>   		d = pci_host_bridge_msi_domain(b);
>>>> 
>>>>   	dev_set_msi_domain(&bus->dev, d);
>>>> +	if (!d)
>>>> +		bus->bus_flags |= PCI_BUS_FLAGS_NO_MSI;
>>> 
>>> Hrm, that might break legacy setups (no irqdomain support). I'd rather
>>> prefer to explicitly tell the pci core at host registration time.
>> 
>> s/might break/ breaks /     Just validated :)
>
> For my own edification, can you point me to the failing case?

Any architecture which selects PCI_MSI_ARCH_FALLBACKS and does not have
irqdomain support runs into:

	if (!d)
		bus->bus_flags |= PCI_BUS_FLAGS_NO_MSI;

which in turn makes pci_msi_supported() return 0 and consequently makes
pci_enable_msi[x]() fail.

Thanks,

        tglx