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Date: Tue, 21 May 2019 10:36:47 +0530 From: Vidya Sagar <vidyas@...dia.com> To: Bjorn Helgaas <helgaas@...nel.org> CC: Christoph Hellwig <hch@...radead.org>, <lorenzo.pieralisi@....com>, <robh+dt@...nel.org>, <mark.rutland@....com>, <thierry.reding@...il.com>, <jonathanh@...dia.com>, <kishon@...com>, <catalin.marinas@....com>, <will.deacon@....com>, <jingoohan1@...il.com>, <gustavo.pimentel@...opsys.com>, <mperttunen@...dia.com>, <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>, <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>, <kthota@...dia.com>, <mmaddireddy@...dia.com>, <sagar.tv@...il.com> Subject: Re: [PATCH V6 02/15] PCI/PME: Export pcie_pme_disable_msi() & pcie_pme_no_msi() APIs 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. >
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