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Date:   Tue, 03 Nov 2020 10:29:17 +0000
From:   Marc Zyngier <maz@kernel.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Frank Wunderlich <frank-w@public-files.de>,
        Ryder Lee <ryder.lee@mediatek.com>,
        linux-mediatek@lists.infradead.org,
        Frank Wunderlich <linux@fw-web.de>,
        linux-kernel@vger.kernel.org,
        Matthias Brugger <matthias.bgg@gmail.com>,
        linux-pci@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: Aw: Re: [PATCH] pci: mediatek: fix warning in msi.h
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On 2020-11-03 10:16, Thomas Gleixner wrote:
> 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.

I pointer that out in [1], together with a potential fix. Not sure if
anything else breaks though.

Thanks,

         M.

[1] 
https://lore.kernel.org/r/336d6588567949029c52ecfbb87660c1@kernel.org/
-- 
Jazz is not dead. It just smells funny...