Re: [PATCH V7 02/15] PCI: Disable MSI for Tegra194 root port

[Vidya Sagar]

On 5/22/2019 1:06 AM, Bjorn Helgaas wrote:
> On Tue, May 21, 2019 at 10:17:26PM +0530, Vidya Sagar wrote:
> > On 5/21/2019 3:57 PM, Thierry Reding wrote:
> > > On Fri, May 17, 2019 at 06:08:33PM +0530, Vidya Sagar wrote:
> > > > Tegra194 rootports don't generate MSI interrupts for PME events and hence
> > > > MSI needs to be disabled for them to avoid root ports service drivers
> > > > registering their respective ISRs with MSI interrupt.
>
> The service drivers (AER, hotplug, etc) don't know whether the
> interrupt is INTx or MSI; they just register their ISRs with
> pcie_device.irq.
>
> The point of this patch is that the PCI core doesn't support devices
> that use MSI and INTx at the same time, and since this device can't
> generate MSI for PME, we have to use INTx for *all* its interrupts.
>
> > > > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
> > > > ---
> > > > Changes since [v6]:
> > > > * This is a new patch
> > > >
> > > >    drivers/pci/quirks.c | 14 ++++++++++++++
> > > >    1 file changed, 14 insertions(+)
> > > >
> > > > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > > > index 0f16acc323c6..28f9a0380df5 100644
> > > > --- a/drivers/pci/quirks.c
> > > > +++ b/drivers/pci/quirks.c
> > > > @@ -2592,6 +2592,20 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_NVIDIA,
> > > >    			PCI_DEVICE_ID_NVIDIA_NVENET_15,
> > > >    			nvenet_msi_disable);
> > > > +/*
> > > > + * Tegra194's PCIe root ports don't generate MSI interrupts for PME events
> > > > + * instead legacy interrupts are generated. Hence, to avoid service drivers
> > > > + * registering their respective ISRs for MSIs, need to disable MSI interrupts
> > > > + * for root ports.
> > > > + */
> > > > +static void disable_tegra194_rp_msi(struct pci_dev *dev)
> > > > +{
> > > > +	dev->no_msi = 1;
> > > > +}
> > > > +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_NVIDIA, 0x1ad0, disable_tegra194_rp_msi);
> > > > +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_NVIDIA, 0x1ad1, disable_tegra194_rp_msi);
> > > > +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_NVIDIA, 0x1ad2, disable_tegra194_rp_msi);
> > > > +
> > >
> > > Later functions in this file seem to use a more consistent naming
> > > pattern, according to which the name for this would become:
> > >
> > > 	pci_quirk_nvidia_tegra194_disable_rp_msi
> > >
> > > Might be worth considering making this consistent.
> > >
> > > This could also be moved to the DWC driver to restrict this to where it
> > > is needed. In either case, this seems like a good solution, so:
> > >
> > > Reviewed-by: Thierry Reding <treding@xxxxxxxxxx>
> > Ok. I'll move it to DWC driver along with name change for the quirk API.
>
> Is there any possibility this hardware would be used in an ACPI
> system?  If so, the quirk should probably stay in drivers/pci/quirks.c
> because the DWC driver would not be present.
Yes. There is a plan to boot kernel through UEFI (using ACPI) on this system.
So, I'll move it to drivers/pci/quirks.c file.

> Either way, please also add some PCIe spec references about this in
> the changelog and a comment in the code about working around this
> issue.  I think the MSI/MSI-X sections that prohibit a device from
> using both INTx and MSI/MSI-X are probably the most pertinent.
Ok. I'll take care of it in the next patch series.

> The reason I want a comment about this is to discourage future
> hardware from following this example because every device that *does*
> follow this example requires a kernel update that would be otherwise
> unnecessary.
Ok. I'll take it up with our hardware engineers to have only MSI/MSI-X interrupts
getting generated for all root port received events.

> Bjorn