linux-kernel - RE: [PATCH] PCI/AER: Enable SERR# forwarding in non ACPI flow

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Date:   Wed, 18 Jul 2018 13:34:20 +0000
From:   Bharat Kumar Gogada <bharatku@...inx.com>
To:     "poza@...eaurora.org" <poza@...eaurora.org>
CC:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci-owner@...r.kernel.org" <linux-pci-owner@...r.kernel.org>
Subject: RE: [PATCH] PCI/AER: Enable SERR# forwarding in non ACPI flow

> On 2018-07-13 19:25, Bharat Kumar Gogada wrote:
> >> > Currently PCI_BRIDGE_CTL_SERR is being enabled only in ACPI flow.
> >> > This bit is required for forwarding errors reported by EP devices
> >> > to upstream device.
> >> > This patch enables SERR# for Type-1 PCI device.
> >> >
> >> > Signed-off-by: Bharat Kumar Gogada
> <bharat.kumar.gogada@...inx.com>
> >> > ---
> >> >  drivers/pci/pcie/aer.c |   23 +++++++++++++++++++++++
> >> >  1 files changed, 23 insertions(+), 0 deletions(-)
> >> >
> >> > diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c index
> >> > a2e8838..943e084 100644
> >> > --- a/drivers/pci/pcie/aer.c
> >> > +++ b/drivers/pci/pcie/aer.c
> >> > @@ -343,6 +343,19 @@ int pci_enable_pcie_error_reporting(struct
> >> > pci_dev
> >> > *dev)
> >> >  	if (!dev->aer_cap)
> >> >  		return -EIO;
> >> >
> >> > +	if (!IS_ENABLED(CONFIG_ACPI) &&
> >> > +	    dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
> >> > +		u16 control;
> >> > +
> >> > +		/*
> >> > +		 * A Type-1 PCI bridge will not forward ERR_ messages
> >> coming
> >> > +		 * from an endpoint if SERR# forwarding is not enabled.
> >> > +		 */
> >> > +		pci_read_config_word(dev, PCI_BRIDGE_CONTROL,
> >> &control);
> >> > +		control |= PCI_BRIDGE_CTL_SERR;
> >> > +		pci_write_config_word(dev, PCI_BRIDGE_CONTROL, control);
> >> > +	}
> >> > +
> >> >  	return pcie_capability_set_word(dev, PCI_EXP_DEVCTL,
> >> > PCI_EXP_AER_FLAGS);  }
> >> > EXPORT_SYMBOL_GPL(pci_enable_pcie_error_reporting);
> >> > @@ -352,6 +365,16 @@ int pci_disable_pcie_error_reporting(struct
> >> > pci_dev *dev)
> >> >  	if (pcie_aer_get_firmware_first(dev))
> >> >  		return -EIO;
> >> >
> >> > +	if (!IS_ENABLED(CONFIG_ACPI) &&
> >> > +	    dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
> >> > +		u16 control;
> >> > +
> >> > +		/* Clear SERR Forwarding */
> >> > +		pci_read_config_word(dev, PCI_BRIDGE_CONTROL,
> >> &control);
> >> > +		control &= ~PCI_BRIDGE_CTL_SERR;
> >> > +		pci_write_config_word(dev, PCI_BRIDGE_CONTROL, control);
> >> > +	}
> >> > +
> >> >  	return pcie_capability_clear_word(dev, PCI_EXP_DEVCTL,
> >> >  					  PCI_EXP_AER_FLAGS);
> >> >  }
> >>
> >>
> >> Should this configuration no be set by Firmware ? why should Linux
> >> dictate it ?
> > Hi Oza, Can you please let us know why this should be set by firmware ?
> > Spec clearly states ERR_CORR,ERR_FATAL/NON FATAL will be forwarded
> > only if this bit is set.
> > If linux AER service is being enabled without checking/setting this
> > bit, then AER service will not do anything even ERR_* is seen on link.
> >
> > Regards,
> > Bharat
> 
> 
> The ERR_* to be forwarded or not to be forwarded could be decision of the
> platform.
> hence I think it is best left to firmware to decide if it want to enable this for
> particular platform.
> 
I'm not aware of other platforms, can you please give an example of a platform 
how it decides to set this in firmware ?

> although,
> There are 2 cases
> Hotplug capable bridge and otherwise.

Yes, what about an RP which supports only AER but doesn't support Hotplug ?
If we have this patch we can set this bit without firmware also.
> 
> 1) If Firmware sets them, I do not think during enumeraion linux will loose
> those settings. 

> 2) I do not see any integration of hotplug with AER currently, so if the PCIe
> switch is plugged into Hotplug capable RP, I am not very sure if this functions
> get called.
> 
> Keith, Lukas and Bjorn any comments ?
Hi all, do you have any inputs on this ?

Regards,
Bharat