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

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Date:   Sun, 01 Nov 2020 21:47:25 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Frank Wunderlich <frank-w@...lic-files.de>
Cc:     Ryder Lee <ryder.lee@...iatek.com>,
        linux-mediatek@...ts.infradead.org,
        Thomas Gleixner <tglx@...utronix.de>,
        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 Sun, 01 Nov 2020 18:27:13 +0000,
Frank Wunderlich <frank-w@...lic-files.de> wrote:
> 
> > Gesendet: Sonntag, 01. November 2020 um 18:54 Uhr
> > Von: "Ryder Lee" <ryder.lee@...iatek.com>
> 
> > Yea, mt7623 (mtk_pcie_soc_v1) does not support MSI, so that's a way to
> > handle it.
> >
> > @Frank, could you help to test it?
> >
> > Ryder
> 
> compiles clean for mt7623/armhf and mt7622/aarch64 so far
> 
> at least bananapi-r2/mt7623 booting is clean now - no warning pcie
> and sata/ahci seems still working as expected. I have a mt7615 card
> in pcie-slot (firmware-load and init without errors) and hdd
> connected to outer sata port (can access partitions witout errors)
> 
> booted r64 too, still see no warning, but have not yet connected
> hdd/pcie-device, but i guess this should not break anything here
> 
> so Marc, if you post the patch separately, you can add my tested-by
> ;) thank you for this

Thinking of it a bit more, I think this is the wrong solution.

PCI MSIs are optional, and not a requirement. I can trivially spin a
VM with PCI devices and yet no MSI capability (yes, it is more
difficult with real HW), and this results in a bunch of warning, none
of which are actually indicative of anything being wrong.

I think the real fix is to get rid of the warnings altogether. If we
could detect that there should be an MSI domain associated with the
device and that it wasn't there, that'd be a good reason to scream.
But on its own, the absence of a MSI domain is not an indication of
anything being amiss.

	M.

-- 
Without deviation from the norm, progress is not possible.