linux-kernel - Re: [PATCH NEXT 6/6] PCI/PORTDRV: Remove ERR_FATAL handling from pcie_portdrv_slot

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Message-ID: <50f38cb058b29f84ca60a19825efd28a@codeaurora.org>
Date:   Mon, 11 Jun 2018 15:31:44 +0530
From:   poza@...eaurora.org
To:     Bjorn Helgaas <helgaas@...nel.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>
Subject: Re: [PATCH NEXT 6/6] PCI/PORTDRV: Remove ERR_FATAL handling from
 pcie_portdrv_slot_reset()

On 2018-06-08 03:04, Bjorn Helgaas wrote:
> On Thu, Jun 07, 2018 at 07:18:03PM +0530, poza@...eaurora.org wrote:
>> On 2018-06-07 11:30, Oza Pawandeep wrote:
>> > We are handling ERR_FATAL by resetting the Link in software,skipping the
>> > driver pci_error_handlers callbacks, removing the devices from the PCI
>> > subsystem, and re-enumerating, as a result of that, no more calling
>> > pcie_portdrv_slot_reset in ERR_FATAL case.
>> >
>> > Signed-off-by: Oza Pawandeep <poza@...eaurora.org>
>> >
>> > diff --git a/drivers/pci/pcie/portdrv_pci.c
>> > b/drivers/pci/pcie/portdrv_pci.c
>> > index 973f1b8..92f5d330 100644
>> > --- a/drivers/pci/pcie/portdrv_pci.c
>> > +++ b/drivers/pci/pcie/portdrv_pci.c
>> > @@ -42,17 +42,6 @@ __setup("pcie_ports=", pcie_port_setup);
>> >
>> >  /* global data */
>> >
>> > -static int pcie_portdrv_restore_config(struct pci_dev *dev)
>> > -{
>> > -	int retval;
>> > -
>> > -	retval = pci_enable_device(dev);
>> > -	if (retval)
>> > -		return retval;
>> > -	pci_set_master(dev);
>> > -	return 0;
>> > -}
>> > -
>> >  #ifdef CONFIG_PM
>> >  static int pcie_port_runtime_suspend(struct device *dev)
>> >  {
>> > @@ -162,14 +151,6 @@ static pci_ers_result_t
>> > pcie_portdrv_mmio_enabled(struct pci_dev *dev)
>> >
>> >  static pci_ers_result_t pcie_portdrv_slot_reset(struct pci_dev *dev)
>> >  {
>> > -	/* If fatal, restore cfg space for possible link reset at upstream */
>> > -	if (dev->error_state == pci_channel_io_frozen) {
>> > -		dev->state_saved = true;
>> > -		pci_restore_state(dev);
>> > -		pcie_portdrv_restore_config(dev);
>> > -		pci_enable_pcie_error_reporting(dev);
>> > -	}
>> > -
>> >  	return PCI_ERS_RESULT_RECOVERED;
>> >  }
>> 
>> 
>> Hi Bjorn,
>> 
>> the above patch removes ERR_FATAL handling from 
>> pcie_portdrv_slot_reset()
>> because now we are handling ERR_FATAL differently than before.
>> 
>> I tried to dig into pcie_portdrv_slot_reset() handling for ERR_FATAL 
>> case
>> where it
>> restores the config space, enable device, set master and enable error
>> reporting....
>> and as far as I understand this is being done for upstream link 
>> (bridges
>> etc..)
>> 
>> why was it done at the first point (I checked the commit description, 
>> but
>> could not really get it)
>> and do we need to handle the same thing in ERR_FATAL now ?
> 
> You mean 4bf3392e0bf5 ("PCI-Express AER implemetation: pcie_portdrv
> error handler"), which added pcie_portdrv_slot_reset()?  I agree, that
> commit log has no useful information.  I don't know any of the history
> behind it.

Hi Bjorn and Keith,

broadcast_error_message()
if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
         .....
         pci_walk_bus(dev->subordinate, cb, &result_data);


so in case of ERR_FATAL, the walk bus is happening on subordinates, and 
if I understand the walk right
then, pcie_portdrv_slot_reset() is called only on BRIDGES/Switches

If is never called on Root-Ports

having said that, now since we are removing the devices (compare to 
previous error callback handling in ERR_FATAL)
I dont see the need of the above code anymore.

because there is nothing to restore to any more. as we are initiating 
re-enumeration.

Regards,
Oza.