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

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
Date: Tue, 03 Nov 2020 09:54:23 +0000	[thread overview]
Message-ID: <901c5eb8bbaa3fe53ddc8f65917e48ef@kernel.org> (raw)
In-Reply-To: <877dr38kt8.fsf@nanos.tec.linutronix.de>

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?

> 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.

> 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.

I'll have a think.

         M.
-- 
Jazz is not dead. It just smells funny...