On 5/20/2019 11:27 PM, Bjorn Helgaas wrote:
On Sat, May 18, 2019 at 07:28:29AM +0530, Vidya Sagar wrote:
On 5/18/2019 12:25 AM, Bjorn Helgaas wrote:
On Fri, May 17, 2019 at 11:23:36PM +0530, Vidya Sagar wrote:
On 5/17/2019 6:54 PM, Bjorn Helgaas wrote:
Do you have "lspci -vvxxx" output for the root ports handy?
If there's some clue in the standard config space that would tell us
that MSI works for some events but not others, we could make the PCI
core pay attention it. That would be the best solution because it
wouldn't require Tegra-specific code.
Here is the output of 'lspci vvxxx' for one of Tegra194's root ports.
Thanks!
This port advertises both MSI and MSI-X, and neither one is enabled.
This particular port doesn't have a slot, so hotplug isn't applicable
to it.
But if I understand correctly, if MSI or MSI-X were enabled and the
port had a slot, the port would generate MSI/MSI-X hotplug interrupts.
But PME and AER events would still cause INTx interrupts (even with
MSI or MSI-X enabled).
Do I have that right? I just want to make sure that the reason for
PME being INTx is a permanent hardware choice and that it's not
related to MSI and MSI-X currently being disabled.
Yes. Thats right. Its hardware choice that our hardware engineers made to
use INTx for PME instead of MSI irrespective of MSI/MSI-X enabled/disabled
in the root port.
Here are more spec references that seem applicable:
- PCIe r4.0, sec 7.7.1.2 (Message Control Register for MSI) says:
MSI Enable – If Set and the MSI-X Enable bit in the MSI-X
Message Control register (see Section 7.9.2) is Clear, the
Function is permitted to use MSI to request service and is
prohibited from using INTx interrupts.
- PCIe r4.0, sec 7.7.2.2 (Message Control Register for MSI-X) says:
MSI-X Enable – If Set and the MSI Enable bit in the MSI Message
Control register (see Section 6.8.1.3) is Clear, the Function is
permitted to use MSI-X to request service and is prohibited from
using INTx interrupts (if implemented).
I read that to mean a device is prohibited from using MSI/MSI-X for
some interrupts and INTx for others. Since Tegra194 cannot use
MSI/MSI-X for PME, it should use INTx for *all* interrupts. That
makes the MSI/MSI-X Capabilities superfluous, and they should be
omitted.
If we set pdev->no_msi for Tegra194, we'll avoid MSI/MSI-X completely,
so we'll assume *all* interrupts including hotplug will be INTx. Will
that work?
Yes. We are fine with having all root port originated interrupts getting generated
through INTx instead of MSI/MSI-X.
