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

["Chocron, Jonathan" <jonnyc@amazon.com>]

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.

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.

> 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
> >