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Date: Wed, 9 May 2018 18:21:11 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: poza@...eaurora.org
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
Philippe Ombredanne <pombredanne@...b.com>,
Thomas Gleixner <tglx@...utronix.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Kate Stewart <kstewart@...uxfoundation.org>,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
Dongdong Liu <liudongdong3@...wei.com>,
Keith Busch <keith.busch@...el.com>, Wei Zhang <wzhang@...com>,
Sinan Kaya <okaya@...eaurora.org>,
Timur Tabi <timur@...eaurora.org>,
linux-pci-owner@...r.kernel.org
Subject: Re: [PATCH v15 3/9] PCI/AER: Handle ERR_FATAL with removal and
re-enumeration of devices
On Wed, May 09, 2018 at 06:44:53PM +0530, poza@...eaurora.org wrote:
> On 2018-05-09 18:37, Bjorn Helgaas wrote:
> > On Tue, May 08, 2018 at 06:53:30PM -0500, Bjorn Helgaas wrote:
> > > On Thu, May 03, 2018 at 01:03:52AM -0400, Oza Pawandeep wrote:
> > > > This patch alters the behavior of handling of ERR_FATAL, where removal
> > > > of devices is initiated, followed by reset link, followed by
> > > > re-enumeration.
> > > >
> > > > So the errors are handled in a different way as follows:
> > > > ERR_NONFATAL => call driver recovery entry points
> > > > ERR_FATAL => remove and re-enumerate
> > > >
> > > > please refer to Documentation/PCI/pci-error-recovery.txt for more details.
> > > >
> > > > Signed-off-by: Oza Pawandeep <poza@...eaurora.org>
> > > >
> > > > diff --git a/drivers/pci/pcie/aer/aerdrv.c b/drivers/pci/pcie/aer/aerdrv.c
> > > > index 779b387..206f590 100644
> > > > --- a/drivers/pci/pcie/aer/aerdrv.c
> > > > +++ b/drivers/pci/pcie/aer/aerdrv.c
> > > > @@ -330,6 +330,13 @@ static pci_ers_result_t aer_root_reset(struct pci_dev *dev)
> > > > reg32 |= ROOT_PORT_INTR_ON_MESG_MASK;
> > > > pci_write_config_dword(dev, pos + PCI_ERR_ROOT_COMMAND, reg32);
> > > >
> > > > + /*
> > > > + * This function is called only on ERR_FATAL now, and since
> > > > + * the pci_report_resume is called only in ERR_NONFATAL case,
> > > > + * the clearing part has to be taken care here.
> > > > + */
> > > > + aer_error_resume(dev);
> > >
> > > I don't understand this part. Previously the ERR_FATAL path looked
> > > like
> > > this:
> > >
> > > do_recovery
> > > reset_link
> > > driver->reset_link
> > > aer_root_reset
> > > pci_reset_bridge_secondary_bus # <-- reset
> > > broadcast_error_message(..., report_resume)
> > > pci_walk_bus(..., report_resume, ...)
> > > report_resume
> > > if (cb == report_resume)
> > > pci_cleanup_aer_uncorrect_error_status
> > > pci_write_config_dword(PCI_ERR_UNCOR_STATUS) # <-- clear
> > > status
> > >
> > > After this patch, it will look like this:
> > >
> > > do_recovery
> > > do_fatal_recovery
> > > pci_cleanup_aer_uncorrect_error_status
> > > pci_write_config_dword(PCI_ERR_UNCOR_STATUS) # <-- clear
> > > status
> > > reset_link
> > > driver->reset_link
> > > aer_root_reset
> > > pci_reset_bridge_secondary_bus # <-- reset
> > > aer_error_resume
> > > pcie_capability_write_word(PCI_EXP_DEVSTA) #
> > > <-- clear more
> > > pci_write_config_dword(PCI_ERR_UNCOR_STATUS) #
> > > <-- clear status
> > >
> > > So if I'm understanding correctly, the new path clears the status too
> > > early, then clears it again (plus clearing DEVSTA, which we didn't do
> > > before) later.
> > >
> > > I would think we would want to leave aer_root_reset() alone, and
> > > just move
> > > the pci_cleanup_aer_uncorrect_error_status() in do_fatal_recovery()
> > > down so
> > > it happens after we call reset_link(). That way the reset/clear
> > > sequence
> > > would be the same as it was before.
> >
> > I've been fiddling with this a bit myself and will post the results to
> > see
> > what you think.
>
>
> ok so you are suggesting to move pci_cleanup_aer_uncorrect_error_status down
> which I can do.
>
> And not to call aer_error_resume, because you think its clearing the status
> again.
>
> following code: calls aer_error_resume.
> pci_broadcast_error_message()
> /*
> * If the error is reported by an end point, we think this
> * error is related to the upstream link of the end point.
> */
> if (state == pci_channel_io_normal)
> /*
> * the error is non fatal so the bus is ok, just
> invoke
> * the callback for the function that logged the
> error.
> */
> cb(dev, &result_data);
> else
> pci_walk_bus(dev->bus, cb, &result_data);
Holy crap, I thought this could not possibly get any more complicated,
but you're right; we do actually call aer_error_resume() today via an
extremely convoluted path:
do_recovery(pci_dev)
broadcast_error_message(..., error_detected, ...)
if (AER_FATAL)
reset_link(pci_dev)
udev = BRIDGE ? pci_dev : pci_dev->bus->self
driver->reset_link(udev)
aer_root_reset(udev)
if (CAN_RECOVER)
broadcast_error_message(..., mmio_enabled, ...)
if (NEED_RESET)
broadcast_error_message(..., slot_reset, ...)
broadcast_error_message(dev, ..., report_resume, ...)
if (BRIDGE)
report_resume
driver->resume
pcie_portdrv_err_resume
device_for_each_child(..., resume_iter)
resume_iter
driver->error_resume
aer_error_resume
pci_cleanup_aer_uncorrect_error_status(pci_dev) # only if BRIDGE
pci_write_config_dword(PCI_ERR_UNCOR_STATUS)
aerdriver is the only port service driver that implements
.error_resume(), and aerdriver only binds to root ports. I can't
really believe all these device_for_each_child()/resume_iter()
gyrations are necessary when this is AER code calling AER code.
Bjorn
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