Hi all,

Since Linux v5.13, we have noticed that following warning splat when
booting Tegra (ARM64) with ACPI ...

[    2.725479] WARNING: CPU: 0 PID: 94 at include/linux/msi.h:264 free_msi_irqs+0x84/0x188
[    2.736137] Modules linked in:
[    2.736147] CPU: 0 PID: 94 Comm: kworker/u16:1 Tainted: G        W         5.12.0-rc2-00008-g658376bd3e5-dirty #36
[    2.736160] Workqueue: nvme-reset-wq nvme_reset_work
[    2.746470] pstate: 60400009 (nZCv daif +PAN -UAO -TCO BTYPE=--)
[    2.757713] pc : free_msi_irqs+0x84/0x188
[    2.757726] lr : __pci_enable_msix_range+0x380/0x530
[    2.757735] sp : ffff800012813b00
[    2.757739] x29: ffff800012813b00
[    2.768371] x28: 00000000ffffffed
[    2.768382] x27: 0000000000000001 x26: 0000000000000000
[    2.768393] x25: ffff0000809362e8 x24: 0000000000000000
[    2.768407] x23: 000000000000000c x22: ffff000080936000
[    2.768418] x21: ffff0000809362e8 x20: ffff0000809362e8
[    2.775320] x19: ffff000080936000
[    2.785950] x18: ffffffffffffffff
[    2.785961] x17: 0000000000000007 x16: 0000000000000001
[    2.785975] x15: ffff800011bf9948
[    2.793997] x14: ffff8000928137e7
[    2.794009] x13: ffff8000128137f5 x12: ffff800011c19640
[    2.794023] x11: fffffffffffe5788 x10: 0000000005f5e0ff
[    2.794034] x9 : 00000000ffffffd0 x8 : 203a737542204f49
[    2.803737] x7 : 444d206465786946 x6 : ffff800011ee1fd7
[    2.803750] x5 : 0000000000000000 x4 : 0000000000000000
[    2.815286] x3 : 00000000ffffffff x2 : ffff0000809362e8
[    2.815300] x1 : ffff0000809362e8 x0 : 0000000000000000
[    2.825270] Call trace:
[    2.825275]  free_msi_irqs+0x84/0x188
[    2.825288]  __pci_enable_msix_range+0x380/0x530
[    2.825299]  pci_alloc_irq_vectors_affinity+0x158/0x168
[    2.825309]  nvme_reset_work+0x214/0x15b8
[    2.829340] dwc-eth-dwmac NVDA1160:00: SPH feature enabled
[    2.832986]  process_one_work+0x1cc/0x360
[    2.833002]  worker_thread+0x48/0x450
[    2.833012]  kthread+0x120/0x150
[    2.833020]  ret_from_fork+0x10/0x18


Bisecting this I found that started to occur because with Linux v5.13,
CONFIG_PCI_MSI_ARCH_FALLBACKS was no longer enabled by default and only
happened to be enabled because Renesas R-Car was enabling it.

When booting with ACPI, I see that when pci_msi_setup_msi_irqs() is
called, it ends up calling arch_setup_msi_irqs() and if
CONFIG_PCI_MSI_ARCH_FALLBACKS  is not enabled, then this will call
WARN_ON_ONCE(1).

So the question is, should this be enabled by default for ARM64? I see
a lot of other architectures enabling this when PCI_MSI is enabled. So
I am wondering if we should be doing something like ...

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1f212b47a48a..4bbd81bab809 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -202,6 +202,7 @@ config ARM64
         select PCI_DOMAINS_GENERIC if PCI
         select PCI_ECAM if (ACPI && PCI)
         select PCI_SYSCALL if PCI
+       select PCI_MSI_ARCH_FALLBACKS if PCI_MSI
         select POWER_RESET
         select POWER_SUPPLY
         select SPARSE_IRQ

Cheers
Jon

-- 
nvpublic