From:   John Garry <john.garry@huawei.com>
Subject: PCI MSI issue for maxcpus=1
To:     Marc Zyngier <maz@kernel.org>, Thomas Gleixner <tglx@linutronix.de>
CC:     chenxiang <chenxiang66@hisilicon.com>,
        Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "liuqi (BA)" <liuqi115@huawei.com>
Message-ID: <78615d08-1764-c895-f3b7-bfddfbcbdfb9@huawei.com>
Date:   Wed, 5 Jan 2022 11:23:47 +0000
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Hi Marc,

Just a heads up, I noticed that commit 4c457e8cb75e ("genirq/msi: 
Activate Multi-MSI early when MSI_FLAG_ACTIVATE_EARLY is set") is 
causing an issue on our arm64 D06 board where the SAS driver probe fails 
for maxcpus=1.

This seems different to issue [0].

So it's the driver call to pci_alloc_irq_vectors_affinity() which errors 
[1]:

[    9.619070] hisi_sas_v3_hw: probe of 0000:74:02.0 failed with error -2

Some details:
- device supports 32 MSI
- min and max msi for that function is 17 and 32, respect.
- affd pre and post are 16 and 0, respect.

I haven't checked to see what the issue is yet and I think that the 
pci_alloc_irq_vectors_affinity() usage is ok...

[0] 
https://lore.kernel.org/lkml/ea730f9b-c635-317d-c70d-4057590b1d1a@huawei.com/
[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c?h=v5.11#n2388

Cheers,
John