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Date:   Wed, 16 May 2018 20:28:39 +0530
From:   poza@codeaurora.org
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     Bjorn Helgaas <bhelgaas@google.com>,
        Philippe Ombredanne <pombredanne@nexb.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        Dongdong Liu <liudongdong3@huawei.com>,
        Keith Busch <keith.busch@intel.com>, Wei Zhang <wzhang@fb.com>,
        Sinan Kaya <okaya@codeaurora.org>,
        Timur Tabi <timur@codeaurora.org>,
        linux-pci-owner@vger.kernel.org
Subject: Re: [PATCH v16 8/9] PCI/DPC: Unify and plumb error handling into DPC
In-Reply-To: <20180516130455.GA233993@bhelgaas-glaptop.roam.corp.google.com>
References: <1526035408-31328-1-git-send-email-poza@codeaurora.org>
 <1526035408-31328-9-git-send-email-poza@codeaurora.org>
 <a497fae20a326bdf67395c907a5b6b0d@codeaurora.org>
 <20180515235632.GB11156@bhelgaas-glaptop.roam.corp.google.com>
 <2ca65f6b38668cfcf553833409ee38e3@codeaurora.org>
 <20180516105236.GA217390@bhelgaas-glaptop.roam.corp.google.com>
 <3822b5ea0b05f9836b991ce18f16a30f@codeaurora.org>
 <20180516130455.GA233993@bhelgaas-glaptop.roam.corp.google.com>
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On 2018-05-16 18:34, Bjorn Helgaas wrote:
> On Wed, May 16, 2018 at 05:45:58PM +0530, poza@codeaurora.org wrote:
>> On 2018-05-16 16:22, Bjorn Helgaas wrote:
>> > On Wed, May 16, 2018 at 01:46:25PM +0530, poza@codeaurora.org wrote:
>> > > On 2018-05-16 05:26, Bjorn Helgaas wrote:
>> > > > On Fri, May 11, 2018 at 05:22:08PM +0530, poza@codeaurora.org wrote:
>> > > > > On 2018-05-11 16:13, Oza Pawandeep wrote:
>> > > > > > DPC driver implements link_reset callback, and calls
>> > > > > > pci_do_fatal_recovery().
>> > > > > >
>> > > > > > Which follows standard path of ERR_FATAL recovery.
>> > > > > >
>> > > > > > Signed-off-by: Oza Pawandeep <poza@codeaurora.org>
>> > > > > >
>> > > > > > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>> > > > > > index 5e8857a..6af7595 100644
>> > > > > > --- a/drivers/pci/pci.h
>> > > > > > +++ b/drivers/pci/pci.h
>> > > > > > @@ -354,7 +354,7 @@ static inline resource_size_t
>> > > > > > pci_resource_alignment(struct pci_dev *dev,
>> > > > > >  void pci_enable_acs(struct pci_dev *dev);
>> > > > > >
>> > > > > >  /* PCI error reporting and recovery */
>> > > > > > -void pcie_do_fatal_recovery(struct pci_dev *dev);
>> > > > > > +void pcie_do_fatal_recovery(struct pci_dev *dev, u32 service);
>> > > > > >  void pcie_do_nonfatal_recovery(struct pci_dev *dev);
>> > > > > >
>> > > > > >  bool pcie_wait_for_link(struct pci_dev *pdev, bool active);
>> > > > > > diff --git a/drivers/pci/pcie/aer/aerdrv_core.c
>> > > > > > b/drivers/pci/pcie/aer/aerdrv_core.c
>> > > > > > index fdfc474..36e622d 100644
>> > > > > > --- a/drivers/pci/pcie/aer/aerdrv_core.c
>> > > > > > +++ b/drivers/pci/pcie/aer/aerdrv_core.c
>> > > > > > @@ -254,7 +254,7 @@ static void handle_error_source(struct pcie_device
>> > > > > > *aerdev,
>> > > > > >  	} else if (info->severity == AER_NONFATAL)
>> > > > > >  		pcie_do_nonfatal_recovery(dev);
>> > > > > >  	else if (info->severity == AER_FATAL)
>> > > > > > -		pcie_do_fatal_recovery(dev);
>> > > > > > +		pcie_do_fatal_recovery(dev, PCIE_PORT_SERVICE_AER);
>> > > > > >  }
>> > > > > >
>> > > > > >  #ifdef CONFIG_ACPI_APEI_PCIEAER
>> > > > > > @@ -321,7 +321,7 @@ static void aer_recover_work_func(struct work_struct
>> > > > > > *work)
>> > > > > >  		if (entry.severity == AER_NONFATAL)
>> > > > > >  			pcie_do_nonfatal_recovery(pdev);
>> > > > > >  		else if (entry.severity == AER_FATAL)
>> > > > > > -			pcie_do_fatal_recovery(pdev);
>> > > > > > +			pcie_do_fatal_recovery(pdev, PCIE_PORT_SERVICE_AER);
>> > > > > >  		pci_dev_put(pdev);
>> > > > > >  	}
>> > > > > >  }
>> > > > > > diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
>> > > > > > index 80ec384..5680c13 100644
>> > > > > > --- a/drivers/pci/pcie/dpc.c
>> > > > > > +++ b/drivers/pci/pcie/dpc.c
>> > > > > > @@ -73,29 +73,31 @@ static void dpc_wait_link_inactive(struct dpc_dev
>> > > > > > *dpc)
>> > > > > >  	pcie_wait_for_link(pdev, false);
>> > > > > >  }
>> > > > > >
>> > > > > > -static void dpc_work(struct work_struct *work)
>> > > > > > +static pci_ers_result_t dpc_reset_link(struct pci_dev *pdev)
>> > > > > >  {
>> > > > > > -	struct dpc_dev *dpc = container_of(work, struct dpc_dev, work);
>> > > > > > -	struct pci_dev *dev, *temp, *pdev = dpc->dev->port;
>> > > > > > -	struct pci_bus *parent = pdev->subordinate;
>> > > > > > -	u16 cap = dpc->cap_pos, ctl;
>> > > > > > -
>> > > > > > -	pci_lock_rescan_remove();
>> > > > > > -	list_for_each_entry_safe_reverse(dev, temp, &parent->devices,
>> > > > > > -					 bus_list) {
>> > > > > > -		pci_dev_get(dev);
>> > > > > > -		pci_dev_set_disconnected(dev, NULL);
>> > > > > > -		if (pci_has_subordinate(dev))
>> > > > > > -			pci_walk_bus(dev->subordinate,
>> > > > > > -				     pci_dev_set_disconnected, NULL);
>> > > > > > -		pci_stop_and_remove_bus_device(dev);
>> > > > > > -		pci_dev_put(dev);
>> > > > > > -	}
>> > > > > > -	pci_unlock_rescan_remove();
>> > > > > > -
>> > > > > > +	struct dpc_dev *dpc;
>> > > > > > +	struct pcie_device *pciedev;
>> > > > > > +	struct device *devdpc;
>> > > > > > +	u16 cap, ctl;
>> > > > > > +
>> > > > > > +	/*
>> > > > > > +	 * DPC disables the Link automatically in hardware, so it has
>> > > > > > +	 * already been reset by the time we get here.
>> > > > > > +	 */
>> > > > > > +
>> > > > > > +	devdpc = pcie_port_find_device(pdev, PCIE_PORT_SERVICE_DPC);
>> > > > > > +	pciedev = to_pcie_device(devdpc);
>> > > > > > +	dpc = get_service_data(pciedev);
>> > > > > > +	cap = dpc->cap_pos;
>> > > > > > +
>> > > > > > +	/*
>> > > > > > +	 * Waiting until the link is inactive, then clearing DPC
>> > > > > > +	 * trigger status to allow the port to leave DPC.
>> > > > > > +	 */
>> > > > > >  	dpc_wait_link_inactive(dpc);
>> > > > > > +
>> > > > > >  	if (dpc->rp_extensions && dpc_wait_rp_inactive(dpc))
>> > > > > > -		return;
>> > > > > > +		return PCI_ERS_RESULT_DISCONNECT;
>> > > > > >  	if (dpc->rp_extensions && dpc->rp_pio_status) {
>> > > > > >  		pci_write_config_dword(pdev, cap + PCI_EXP_DPC_RP_PIO_STATUS,
>> > > > > >  				       dpc->rp_pio_status);
>> > > > > > @@ -108,6 +110,17 @@ static void dpc_work(struct work_struct *work)
>> > > > > >  	pci_read_config_word(pdev, cap + PCI_EXP_DPC_CTL, &ctl);
>> > > > > >  	pci_write_config_word(pdev, cap + PCI_EXP_DPC_CTL,
>> > > > > >  			      ctl | PCI_EXP_DPC_CTL_INT_EN);
>> > > > > > +
>> > > > > > +	return PCI_ERS_RESULT_RECOVERED;
>> > > > > > +}
>> > > > > > +
>> > > > > > +static void dpc_work(struct work_struct *work)
>> > > > > > +{
>> > > > > > +	struct dpc_dev *dpc = container_of(work, struct dpc_dev, work);
>> > > > > > +	struct pci_dev *pdev = dpc->dev->port;
>> > > > > > +
>> > > > > > +	/* From DPC point of view error is always FATAL. */
>> > > > > > +	pcie_do_fatal_recovery(pdev, PCIE_PORT_SERVICE_DPC);
>> > > > > >  }
>> > > > > >
>> > > > > >  static void dpc_process_rp_pio_error(struct dpc_dev *dpc)
>> > > > > > @@ -288,6 +301,7 @@ static struct pcie_port_service_driver dpcdriver = {
>> > > > > >  	.service	= PCIE_PORT_SERVICE_DPC,
>> > > > > >  	.probe		= dpc_probe,
>> > > > > >  	.remove		= dpc_remove,
>> > > > > > +	.reset_link	= dpc_reset_link,
>> > > > > >  };
>> > > > > >
>> > > > > >  static int __init dpc_service_init(void)
>> > > > > > diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>> > > > > > index 33a16b1..29ff148 100644
>> > > > > > --- a/drivers/pci/pcie/err.c
>> > > > > > +++ b/drivers/pci/pcie/err.c
>> > > > > > @@ -185,7 +185,7 @@ static pci_ers_result_t default_reset_link(struct
>> > > > > > pci_dev *dev)
>> > > > > >  	return PCI_ERS_RESULT_RECOVERED;
>> > > > > >  }
>> > > > > >
>> > > > > > -static pci_ers_result_t reset_link(struct pci_dev *dev)
>> > > > > > +static pci_ers_result_t reset_link(struct pci_dev *dev, u32 service)
>> > > > > >  {
>> > > > > >  	struct pci_dev *udev;
>> > > > > >  	pci_ers_result_t status;
>> > > > > > @@ -200,7 +200,7 @@ static pci_ers_result_t reset_link(struct pci_dev
>> > > > > > *dev)
>> > > > > >  	}
>> > > > > >
>> > > > > >  	/* Use the aer driver of the component firstly */
>> > > > > > -	driver = pcie_port_find_service(udev, PCIE_PORT_SERVICE_AER);
>> > > > > > +	driver = pcie_port_find_service(udev, service);
>> > > > > >
>> > > > > >  	if (driver && driver->reset_link) {
>> > > > > >  		status = driver->reset_link(udev);
>> > > > > > @@ -287,7 +287,7 @@ static pci_ers_result_t
>> > > > > > broadcast_error_message(struct pci_dev *dev,
>> > > > > >   * followed by re-enumeration of devices.
>> > > > > >   */
>> > > > > >
>> > > > > > -void pcie_do_fatal_recovery(struct pci_dev *dev)
>> > > > > > +void pcie_do_fatal_recovery(struct pci_dev *dev, u32 service)
>> > > > > >  {
>> > > > > >  	struct pci_dev *udev;
>> > > > > >  	struct pci_bus *parent;
>> > > > > > @@ -313,7 +313,7 @@ void pcie_do_fatal_recovery(struct pci_dev *dev)
>> > > > > >  		pci_dev_put(pdev);
>> > > > > >  	}
>> > > > > >
>> > > > > > -	result = reset_link(udev);
>> > > > > > +	result = reset_link(udev, service);
>> > > > > >
>> > > > > >  	if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
>> > > > > >  		/*
>> > > > > > diff --git a/include/linux/aer.h b/include/linux/aer.h
>> > > > > > index 8f87bbe..0c506fe 100644
>> > > > > > --- a/include/linux/aer.h
>> > > > > > +++ b/include/linux/aer.h
>> > > > > > @@ -14,6 +14,7 @@
>> > > > > >  #define AER_NONFATAL			0
>> > > > > >  #define AER_FATAL			1
>> > > > > >  #define AER_CORRECTABLE			2
>> > > > > > +#define DPC_FATAL			4
>> > > >
>> > > > I think DPC_FATAL can be 3, since these values are not used as a bit
>> > > > mask.
>> > > >
>> > > > > >  struct pci_dev;
>> > > > >
>> > > > >
>> > > > > Hi Bjorn,
>> > > > >
>> > > > >
>> > > > > I have addressed all the comments, and I hope we are heading towards
>> > > > > closure.
>> > > > >
>> > > > > I just figure that pcie_do_fatal_recovery  (which is getting
>> > > > > executed for
>> > > > > DPC as well)
>> > > > >
>> > > > > if (result == PCI_ERS_RESULT_RECOVERED) {
>> > > > >                 if (pcie_wait_for_link(udev, true))
>> > > > >                         pci_rescan_bus(udev->bus);
>> > > > >                 pci_info(dev, "Device recovery successful\n");
>> > > > >         }
>> > > > >
>> > > > > I have to correct it to
>> > > > >
>> > > > > if (service==AER  && result == PCI_ERS_RESULT_RECOVERED) {
>> > > > >                 if (pcie_wait_for_link(udev, true))
>> > > > >                         pci_rescan_bus(udev->bus);
>> > > > >                 pci_info(dev, "Device recovery successful\n");
>> > > > >         }
>> > > >
>> > > > This patch is mostly a restructuring of DPC and doesn't really change
>> > > > its
>> > > > behavior.  DPC didn't previously call pcie_wait_for_link() or
>> > > > pci_rescan_bus(), so I agree that adding the "service==AER" test will
>> > > > help preserve the existing DPC behavior.
>> > > >
>> > > > However, the rescan should happen with DPC *somewhere* and we should
>> > > > clarify where that is.  Maybe for now we only need a comment about where
>> > > > that happens.  Ideally, we could eventually converge this so the same
>> > > > mechanism is used for AER and DPC, so we wouldn't need a test like
>> > > > "service=AER".
>> >
>> > Please still add a comment here about why the rescan behavior is
>> > different.
>> >
>> > > I am sorry I pasted the wrong snippet.
>> > > following needs to be fixed in v17.
>> > > from:
>> > >    if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
>> > >                 /*
>> > >                  * If the error is reported by a bridge, we think
>> > > this error
>> > >                  * is related to the downstream link of the bridge,
>> > > so we
>> > >                  * do error recovery on all subordinates of the bridge
>> > > instead
>> > >                  * of the bridge and clear the error status of the
>> > > bridge.
>> > >                  */
>> > >                 pci_walk_bus(dev->subordinate, report_resume,
>> > > &result_data);
>> > >                 pci_cleanup_aer_uncorrect_error_status(dev);
>> > >         }
>> > >
>> > >
>> > > to
>> > >
>> > >    if (service==AER  && dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
>> > >                 /*
>> > >                  * If the error is reported by a bridge, we think
>> > > this error
>> > >                  * is related to the downstream link of the bridge,
>> > > so we
>> > >                  * do error recovery on all subordinates of the bridge
>> > > instead
>> > >                  * of the bridge and clear the error status of the
>> > > bridge.
>> > >                  */
>> > >                 pci_walk_bus(dev->subordinate, report_resume,
>> > > &result_data);
>> > >                 pci_cleanup_aer_uncorrect_error_status(dev);
>> > >         }
>> > >
>> > > this is only needed in case of AER.
>> >
>> > Oh, I missed this before.  It makes sense to clear the AER status
>> > here, but why do we need to call report_resume()?  We just called all
>> > the driver .remove() methods and detached the drivers from the
>> > devices.  So I don't think report_resume() will do anything
>> > ("dev->driver" should be NULL) except set the dev->error_state to
>> > pci_channel_io_normal.  We probably don't need that because we didn't
>> > change error_state in this fatal error path.
>> 
>> if you remember, the path ends up calling
>> aer_error_resume
>> 
>> the existing code ends up calling aer_error_resume as follows.
>> 
>> 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)
>> 
>> hence I think we have to call it in order to clear the root port
>> PCI_ERR_UNCOR_STATUS and PCI_EXP_DEVSTA.
>> makes sense ?
> 
> I know I sent you the call graph above, so you would think I might
> understand it, but you would be mistaken :)  This still doesn't make
> sense to me.
> 
> I think your point is that we need to call aer_error_resume().  That
> is the aerdriver.error_resume() method.  The AER driver only binds to
> root ports.
> 
> This path:
> 
>   pcie_do_fatal_recovery
>     pci_walk_bus(dev->subordinate, report_resume, &result_data)
> 
> calls report_resume() for every device on the dev->subordinate bus
> (and for anything below those devices).  There are no root ports on
> that dev->subordinate bus, because root ports are always on a root
> bus, never on a subordinate bus.
> 
> So I don't see how report_resume() can ever get to aer_error_resume().
> Can you instrument that path and verify that it actually does get
> there somehow?


you are right....the call
pci_walk_bus(dev->subordinate, report_resume, &result_data);
does not call aer_error_resume()

but
pci_walk_bus(udev->bus, report_resume, &result_data);
does call aer_error_resume()

now if you look at the comment of the function:
/**
  * aer_error_resume - clean up corresponding error status bits
  * @dev: pointer to Root Port's pci_dev data structure
  *
  * Invoked by Port Bus driver during nonfatal recovery.
  */

it is invoked during nonfatal recovery.
but the code handles both fatal and nonfatal clearing of error bits.

if (dev->error_state == pci_channel_io_normal)
		status &= ~mask; /* Clear corresponding nonfatal bits */
	else
		status &= mask; /* Clear corresponding fatal bits */
	pci_write_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, status);


so the question is, should we not call aer_error_resume during fatal 
recovery ?
so that it clears the root port status, if of course the error is 
triggered by AER running agent (RP, Switch)

Regards,
Oza.