On Wed, Jul 24, 2024 at 02:10:30PM -0500, Bjorn Helgaas wrote:
> On Wed, Jul 24, 2024 at 10:00:40AM -0700, Nirmal Patel wrote:
> > VMD does not support legacy interrupts for devices downstream from a
> > VMD endpoint. So initialize the PCI_INTERRUPT_LINE to 0 for these
> > devices to ensure we don't try to set up a legacy irq for them.
>
> s/legacy interrupts/INTx/
> s/legacy irq/INTx/
>
> > Note: This patch was proposed by Jim, I am trying to upstream it.
> >
> > Signed-off-by: Jim Harris <james.r.harris@xxxxxxxxx>
> > Signed-off-by: Nirmal Patel <nirmal.patel@xxxxxxxxxxxxxxx>
> > ---
> > arch/x86/pci/fixup.c | 14 ++++++++++++++
> > 1 file changed, 14 insertions(+)
> >
> > diff --git a/arch/x86/pci/fixup.c b/arch/x86/pci/fixup.c
> > index b33afb240601..a3b34a256e7f 100644
> > --- a/arch/x86/pci/fixup.c
> > +++ b/arch/x86/pci/fixup.c
> > @@ -653,6 +653,20 @@ static void quirk_no_aersid(struct pci_dev *pdev)
> > DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_INTEL, PCI_ANY_ID,
> > PCI_CLASS_BRIDGE_PCI, 8, quirk_no_aersid);
> >
> > +#if IS_ENABLED(CONFIG_VMD)
> > +/*
> > + * VMD does not support legacy interrupts for downstream devices.
> > + * So PCI_INTERRPUT_LINE needs to be initialized to 0 to ensure OS
> > + * doesn't try to configure a legacy irq.
>
> s/legacy interrupts/INTx/
> s/PCI_INTERRPUT_LINE/PCI_INTERRUPT_LINE/
>
> > + */
> > +static void quirk_vmd_interrupt_line(struct pci_dev *dev)
> > +{
> > + if (is_vmd(dev->bus))
> > + pci_write_config_byte(dev, PCI_INTERRUPT_LINE, 0);
> > +}
> > +DECLARE_PCI_FIXUP_HEADER(PCI_ANY_ID, PCI_ANY_ID, quirk_vmd_interrupt_line);
>
> A quirk for every PCI device, even on systems without VMD, seems like
> kind of a clumsy way to deal with this.
>
> Conceptually, I would expect a host bridge driver (VMD acts like a
> host bridge in this case) to know whether it supports INTx, and if the
> driver knows it doesn't support INTx or it has no _PRT or DT
> description of INTx routing to use, an attempt to configure INTx
> should just fail naturally.
>
> I don't claim this is how host bridge drivers actually work; I just
> think it's the way they *should* work.
>
Absolutely! This patch is fixing the issue in a wrong place. There are existing
DT based host bridge drivers that disable INTx due to lack of hardware
capability. The driver just need to nullify pci_host_bridge::map_irq callback.
- Mani
--
மணிவண்ணன் சதாசிவம்
