linux-kernel - Re: [PATCH v2] PCI/AER: Enable SERR# forwarding in non ACPI flow

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Date:   Mon, 10 Sep 2018 11:40:02 +0530
From:   poza@...eaurora.org
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        bhelgaas@...gle.com, rgummal@...inx.com,
        linux-pci-owner@...r.kernel.org
Subject: Re: [PATCH v2] PCI/AER: Enable SERR# forwarding in non ACPI flow

On 2018-09-06 01:40, Bjorn Helgaas wrote:
> On Thu, Aug 09, 2018 at 08:41:27PM +0530, poza@...eaurora.org wrote:
>> On 2018-08-09 20:27, Bharat Kumar Gogada wrote:
>> > As per Figure 6-3 in PCIe r4.0, sec 6.2.6, ERR_ messages
>> > will be forwarded from the secondary interface to the primary interface,
>> > if the SERR# Enable bit in the Bridge Control register is set.
>> > Currently PCI_BRIDGE_CTL_SERR is being enabled only in
>> > ACPI flow.
>> > This patch enables PCI_BRIDGE_CTL_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..4fb0d24 100644
>> > --- a/drivers/pci/pcie/aer.c
>> > +++ b/drivers/pci/pcie/aer.c
>> > @@ -343,6 +343,20 @@ int pci_enable_pcie_error_reporting(struct pci_dev
>> > *dev)
>> >  	if (!dev->aer_cap)
>> >  		return -EIO;
>> >
>> > +	if (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);
>> > +		if (!(control & PCI_BRIDGE_CTL_SERR)) {
>> > +			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 +366,15 @@ int pci_disable_pcie_error_reporting(struct pci_dev
>> > *dev)
>> >  	if (pcie_aer_get_firmware_first(dev))
>> >  		return -EIO;
>> >
>> > +	if (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);
>> >  }
>> 
>> 
>> Hi Bjorn,
>> 
>> I made some comments on patchv1., same I am putting it across here.
>> 
>> what about hot-plug case ?
>> should not aer_init() call pci_enable_pcie_error_reporting() for all
>> the downstream pci_dev ?
>> and remove all the calls from drivers..
>> aer_init will be called for each device (pci_dev) while pciehp does
>> re-enumeration.
>> so probable we might want to call pci_enable_pcie_error_reporting()
>> but that dictates the design where AER framework is taking decision to
>> enable error reporting on behalf of drivers as well.
>> but thats fine I think, if drivers do not want to participate then 
>> they have
>> to call  pci_disable_pcie_error_reporting explicitly.
>> does this make sense ?
> 
> I just replied to the original patch; sorry, I forgot to add you to
> the cc list.  Bharat, when people respond to your v<N> patch, can you
> please add them (and anybody else *they* added) to the cc list when
> you post your v<N+1> patch?
> 
> If we set PCI_BRIDGE_CTL_SERR in the pci_configure_device() path,
> would that address your comments?

yes, that should do.

> 
> There's still a separate question of where and how we should configure
> the error bits in PCI_EXP_DEVCTL (currently done in
> pci_enable_pcie_error_reporting()).
> 
> Bjorn