linux-kernel - Re: [PATCH v4] PCI/AER: Enable error reporting for all ports

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Date:   Fri, 19 Oct 2018 08:58:20 -0600
From:   Keith Busch <keith.busch@...el.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Jon Derrick <jonathan.derrick@...el.com>,
        Dongdong Liu <liudongdong3@...wei.com>,
        Sinan Kaya <okaya@...nel.org>,
        Oza Pawandeep <poza@...eaurora.org>,
        Matthew Wilcox <willy@...radead.org>,
        Lukas Wunner <lukas@...ner.de>, Christoph Hellwig <hch@....de>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] PCI/AER: Enable error reporting for all ports

On Thu, Oct 18, 2018 at 08:11:35PM -0500, Bjorn Helgaas wrote:
> On Thu, Oct 18, 2018 at 05:03:13PM -0600, Keith Busch wrote:
> > On Thu, Oct 18, 2018 at 03:53:58PM -0500, Bjorn Helgaas wrote:
> > > Change the AER service driver so it binds to *all* PCIe Ports,
> > > including Switch Upstream and Downstream Ports.  Enable AER error
> > > reporting for all these Ports, but not for any children.
> > 
> > I'm looking at this again and think enabling/disabling error
> > reporting for ports is the responsibility of the port driver, not
> > the AER service.
> 
> That's an interesting idea.  Can you expand on this a little more?
> Why is it the responsibility of the port driver?
> 
> Do you think pci_enable_pcie_error_reporting() shouldn't be part of
> the AER service because it updates the Device Control register, which
> is in the PCIe Capability, not the AER Capability?
> 
> What about pci_aer_clear_device_status(), which clears Device Status,
> which is also in the PCIe Capability?

I was comparing how other end device driver's enable this, and they all call
pci_enable_pcie_error_reporting() somewhere along their pci_driver->probe
path. With that in mind, are ports special compared to end devices for this
particular feature?
 
> > The following should do the same as this patch, but without making
> > AER driver handle non-root ports.  The report enabling/disabling
> > functions are already stubbed for '!CONFIG_PCIE_AER' and have checks
> > for aer_cap and firmware first.
> 
> If we thought we should enable error reporting *always*, regardless of
> whether the AER service is enabled, this would make perfect sense to
> me, and I might suggest doing it in an even more generic place like
> pci_configure_device() or pci_init_capabilities().

There are unfortunately still pci_driver instances that don't implement
the err_handler callbacks, and may cause problems if we enable error
reporting in the device when its driver isn't capable of reacting to them.

If it wasn't for that, I think it would make more sense to move this
responsibility from drivers to the pci core.

> But that doesn't seem like where you're headed.  It seems like you
> still only want error reporting enabled when CONFIG_PCIEAR=y.  If
> that's the case, it seems like doing it in portdrv only obfuscates the
> connection with AER.  When CONFIG_PCIEAER is unset, the portdrv code
> *looks* like it's doing something but it's really not because of the
> #ifdef magic.

Right, but that's no different than every other Linux pci_driver. The
component that provides the pci_driver.err_handler should be responsible
for requesting to enable device error reporting, and that's provided by
the port driver, not AER.