Re: [PATCH] PCI/AER: save/restore AER registers during suspend/resume

[Keith Busch <kbusch@kernel.org>]

On Fri, Jul 26, 2019 at 02:00:05AM -0700, Patel, Mayurkumar wrote:
> > The call to pci_save_state most likely occurs long before a user has an
> > opportunity to alter these regsiters, though. Won't this just restore
> > what was previously there, and not the state you changed it to?
> 
> 
> There were two things (not sure to call them issues),
> 1. PCI_ERR_ROOT_COMMAND resets to 0  during S3 entry/exit, which disables AER interrupt trigger
> if AER happens on Endpoint after resume.
> 
> Also specified in spec. NCB-PCI_Express_Base_4.0r1.0_September-27-2017-c.pdf in
> chapter 7.8.4.9 Root Error Command Register (Offset 2Ch) - in bitfields descriptions.
> i.e. Correctable Error Reporting Enable – When Set, this bit enables the generation of an interrupt when
> a correctable error is reported by any of the Functions in the Hierarchy Domain associated with this Root Port.
> 
> 2. Root port resets to its default configuration of UNCOR_MASK/SEVER/COR_MASK register bits after system resume.
> This influences user configurations, how errors shall be treated if AER happens on root port itself due to Device (for example
> Endpoint not answering which results in completion timeouts on root ports).
> 
> Following is one example scenario which can handled with this patch.
> - user configures AER registers using setpci certain masks and severity based on debug requirements. This can be applied on Root port of EP.
> - triggers system test which includes S3 entry/exit cycles.
> - system enters s3 -> AER registers settings are saved which has been configured by users.
> - system exits s3 -> AER registers settings are restored which has been configured by users.

Right, I was just more curious *where* the aer state was being saved
during suspend since pci port driver only saves state during probe. This
patch must be relying on the generic pci-driver's power management. I
think that works, but I just didn't realize initially that we're relying
on that path.

> > You are allocating the capability save buffer in aer_probe(), so this
> > save/restore applies only to root ports. But you mention above that you
> > want to restore end devices, right?
> 
> That’s correct. I agree that my commit message was not so explicit.
> But Since I included PCI_ERR_ROOT_COMMAND register for save/restore which is specific to Root ports only & I thought
> endpoint drivers can handle to save/restore (UNCOR_MASK/SEVER/COR_MASK) themselves with its suspend/resume functions.
> 
> However I am fine to move pci_add_ext_cap_save_buffer() to some other function so
> that it also save/restores UNCOR_MASK/SEVER/COR_MASK registers for endpoints and
> if it's not useful to save/restore MASK & SEVER registers  then also fine to remove them
> and just restore PCI_ERR_ROOT_COMMAND & ECRC settings.  Please let me know.

If users are changing default settings that you want to preserve, that
reason should apply to bridges and endpoints too, so I think you ought
to allocate the save buffer for this capability for all devices that
support it in in pci_aer_init(). Just make sure to check the device type
in save/restore so you're not accessing root port specific registers.