Re: [PATCH v3 4/8] PCI: Add quirk to disable MSI-X support for Amazon's Annapurna Labs Root Port

[Andrew Murray <andrew.murray@arm.com>]

On Tue, Aug 20, 2019 at 02:52:30PM +0000, Chocron, Jonathan wrote:
> On Mon, 2019-08-19 at 19:23 +0100, Andrew Murray wrote:
> > On Tue, Jul 23, 2019 at 12:25:29PM +0300, Jonathan Chocron wrote:
> > > The Root Port (identified by [1c36:0032]) doesn't support MSI-X. On
> > > some
> > 
> > Shouldn't this read [1c36:0031]?
> > 
> Indeed. Thanks for catching this.
> 
> > 
> > > platforms it is configured to not advertise the capability at all,
> > > while
> > > on others it (mistakenly) does. This causes a panic during
> > > initialization by the pcieport driver, since it tries to configure
> > > the
> > > MSI-X capability. Specifically, when trying to access the MSI-X
> > > table
> > > a "non-existing addr" exception occurs.
> > > 
> > > Example stacktrace snippet:
> > > 
> > > [    1.632363] SError Interrupt on CPU2, code 0xbf000000 -- SError
> > > [    1.632364] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.2.0-rc1-
> > > Jonny-14847-ge76f1d4a1828-dirty #33
> > > [    1.632365] Hardware name: Annapurna Labs Alpine V3 EVP (DT)
> > > [    1.632365] pstate: 80000005 (Nzcv daif -PAN -UAO)
> > > [    1.632366] pc : __pci_enable_msix_range+0x4e4/0x608
> > > [    1.632367] lr : __pci_enable_msix_range+0x498/0x608
> > > [    1.632367] sp : ffffff80117db700
> > > [    1.632368] x29: ffffff80117db700 x28: 0000000000000001
> > > [    1.632370] x27: 0000000000000001 x26: 0000000000000000
> > > [    1.632372] x25: ffffffd3e9d8c0b0 x24: 0000000000000000
> > > [    1.632373] x23: 0000000000000000 x22: 0000000000000000
> > > [    1.632375] x21: 0000000000000001 x20: 0000000000000000
> > > [    1.632376] x19: ffffffd3e9d8c000 x18: ffffffffffffffff
> > > [    1.632378] x17: 0000000000000000 x16: 0000000000000000
> > > [    1.632379] x15: ffffff80116496c8 x14: ffffffd3e9844503
> > > [    1.632380] x13: ffffffd3e9844502 x12: 0000000000000038
> > > [    1.632382] x11: ffffffffffffff00 x10: 0000000000000040
> > > [    1.632384] x9 : ffffff801165e270 x8 : ffffff801165e268
> > > [    1.632385] x7 : 0000000000000002 x6 : 00000000000000b2
> > > [    1.632387] x5 : ffffffd3e9d8c2c0 x4 : 0000000000000000
> > > [    1.632388] x3 : 0000000000000000 x2 : 0000000000000000
> > > [    1.632390] x1 : 0000000000000000 x0 : ffffffd3e9844680
> > > [    1.632392] Kernel panic - not syncing: Asynchronous SError
> > > Interrupt
> > > [    1.632393] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.2.0-rc1-
> > > Jonny-14847-ge76f1d4a1828-dirty #33
> > > [    1.632394] Hardware name: Annapurna Labs Alpine V3 EVP (DT)
> > > [    1.632394] Call trace:
> > > [    1.632395]  dump_backtrace+0x0/0x140
> > > [    1.632395]  show_stack+0x14/0x20
> > > [    1.632396]  dump_stack+0xa8/0xcc
> > > [    1.632396]  panic+0x140/0x334
> > > [    1.632397]  nmi_panic+0x6c/0x70
> > > [    1.632398]  arm64_serror_panic+0x74/0x88
> > > [    1.632398]  __pte_error+0x0/0x28
> > > [    1.632399]  el1_error+0x84/0xf8
> > > [    1.632400]  __pci_enable_msix_range+0x4e4/0x608
> > > [    1.632400]  pci_alloc_irq_vectors_affinity+0xdc/0x150
> > > [    1.632401]  pcie_port_device_register+0x2b8/0x4e0
> > > [    1.632402]  pcie_portdrv_probe+0x34/0xf0
> > > 
> > > Signed-off-by: Jonathan Chocron <jonnyc@amazon.com>
> > > Reviewed-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
> > > ---
> > >  drivers/pci/quirks.c | 15 +++++++++++++++
> > >  1 file changed, 15 insertions(+)
> > > 
> > > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > > index 23672680dba7..11f843aa96b3 100644
> > > --- a/drivers/pci/quirks.c
> > > +++ b/drivers/pci/quirks.c
> > > @@ -2925,6 +2925,21 @@
> > > DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_ATTANSIC, 0x10a1,
> > >  			quirk_msi_intx_disable_qca_bug);
> > >  DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_ATTANSIC, 0xe091,
> > >  			quirk_msi_intx_disable_qca_bug);
> > > +
> > > +/*
> > > + * Amazon's Annapurna Labs 1c36:0031 Root Ports don't support MSI-
> > > X, so it
> > > + * should be disabled on platforms where the device (mistakenly)
> > > advertises it.
> > > + *
> > > + * The 0031 device id is reused for other non Root Port device
> > > types,
> > > + * therefore the quirk is registered for the PCI_CLASS_BRIDGE_PCI
> > > class.
> > > + */
> > > +static void quirk_al_msi_disable(struct pci_dev *dev)
> > > +{
> > > +	dev->no_msi = 1;
> > > +	pci_warn(dev, "Disabling MSI-X\n");
> > 
> > This will disable both MSI and MSI-X support - is this really the
> > intention
> > here? Do the root ports support MSI and legacy, or just legacy?
> > 
> The HW should support MSI, but we currently don't have a use case for
> it so it hasn't been tested and therefore we are okay with disabling
> it.

OK - then the commit message and comment (for quirk_al_msi_disable) should
probably be updated to reflect this. Especially given that the device id
may be used on other device types - implying that a use-case for this
may later arise.

> 
> For future knowledge, how can just MSI-X be disabled?
> I see that in pcie_port_enable_irq_vec(), the pcieport driver calls
> pci_alloc_irq_vectors() with PCI_IRQ_MSIX | PCI_IRQ_MSI. And
> internally, both __pci_enable_msix_range() and __pci_enable_msi_range()
> use pci_msi_supported() which doesn't differentiate between MSI and
> MSI-x.

The documentation [1] would suggest that once upon a time pci_disable_msix
was used - but now should let pci_alloc_irq_vectors cap the max number
of vectors. However in your case it's the PCIe port driver that is attempting
to allocate MSI-X's and so the solution isn't an obvious one.

Setting dev->msix_enabled to false (i.e. through pci_disable_msix) would
result in an un-necessary WARN_ON_ONCE. I think you'd need to ensure
devi->msix_cap is NULL (which makes sense as your hardware shouldn't be
exposing this capability).

I guess the right way of achieving this would be through a quirk, though you'd
be the first to do this and you'd have to ensure the quirk runs before
anyone tests for msix_cap.

That's my view, though others may have different suggestions.

[1] Documentation/PCI/msi-howto.rst

Thanks,

Andrew Murray

> 
> > Thanks,
> > 
> > Andrew Murray
> > 
> > > +}
> > > +DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_AMAZON_ANNAPURNA_LABS,
> > > 0x0031,
> > > +			      PCI_CLASS_BRIDGE_PCI, 8,
> > > quirk_al_msi_disable);
> > >  #endif /* CONFIG_PCI_MSI */
> > >  
> > >  /*
> > > -- 
> > > 2.17.1
> > >