linux-kernel - Re: [PATCH V6 02/15] PCI/PME: Export pcie_pme_disable_msi() & pcie_pme_no

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Date:   Thu, 16 May 2019 08:34:26 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Vidya Sagar <vidyas@...dia.com>
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 Tue, May 14, 2019 at 09:00:19AM +0530, Vidya Sagar wrote:
> On 5/13/2019 12:55 PM, Christoph Hellwig wrote:
> > On Mon, May 13, 2019 at 10:36:13AM +0530, Vidya Sagar wrote:
> > > Export pcie_pme_disable_msi() & pcie_pme_no_msi() APIs to enable drivers
> > > using these APIs be able to build as loadable modules.
> > 
> > But this is a global setting.  If you root port is broken you need
> > a per-rootport quirk instead.
> > 
> There is nothing broken in Tegra194 root port as such, rather, this
> is more of software configuration choice and we are going with
> legacy interrupts than MSI interrupts (as Tegra194 doesn't support
> raising PME interrupts through MSI and please note that this doesn't
> mean root port is broken).

I think the port *is* broken.  PCIe r4.0, sec 6.1.6, says

  If the Root Port is enabled for edge-triggered interrupt signaling
  using MSI or MSI-X, an interrupt message must be sent every time the
  logical AND of the following conditions transitions from FALSE to
  TRUE:

    * The associated vector is unmasked (not applicable if MSI does
      not support PVM).

    * The PME Interrupt Enable bit in the Root Control register is set
      to 1b.

    * The PME Status bit in the Root Status register is set.

The Tegra194 root port advertises MSI support, so the above should
apply.

> Since Tegra194 has only Synopsys DesignWare core based host
> controllers and not any other hosts, I think it is fine to call this
> API in driver.

It's fine to add a per-device quirk to set pdev->no_msi or something
similar.

Bjorn