Re: [PATCH v3 0/2] PCI: Reduce FLR delay to 10ms for MSFT devices

[Graham Whyte <grwhyte@linux.microsoft.com>]

On 6/11/2025 12:23 AM, Niklas Cassel wrote:
> On Tue, Jun 10, 2025 at 08:27:12PM -0700, Christoph Hellwig wrote:
>> On Wed, Jun 11, 2025 at 12:05:50AM +0000, grwhyte@linux.microsoft.com wrote:
>>> From: Graham Whyte <grwhyte@linux.microsoft.com>
>>>
>>> Add a new flr_delay member of the pci_dev struct to allow customization of
>>> the delay after FLR for devices that do not support immediate readiness
>>> or readiness time reporting. The main scenario this addresses is VF
>>> removal and rescan during runtime repairs and driver updates, which,
>>> if fixed to 100ms, introduces significant delays across multiple VFs.
>>> These delays are unnecessary for devices that complete the FLR well
>>> within this timeframe.
>>
>> Please work with the PCIe SIG to have a standard capability for this
>> instead of piling up hacks like this quirk.
> 
> There is already some support in PCIe for this.
> 
> For Conventional Reset, see PCIe 6.0, section 6.6.1, there is the
> "Readiness Time Reporting Extended Capability":
> "For a Device that implements the Readiness Time Reporting Extended Capability,
> and has reported a Reset Time shorter than 100ms, software is permitted to send
> a Configuration Request to the Device after waiting the reported Reset Time
> from Conventional Reset."
> 
> 
> For FLR, see PCIe 6.0, section 6.6.2, there is the "Function Readiness Status":
> "After an FLR has been initiated by writing a 1b to the Initiate Function Level
> Reset bit, the Function must complete the FLR within 100 ms. [...] If Function
> Readiness Status (FRS - see § Section 6.22.2 ) is implemented, then system
> software is permitted to issue Configuration Requests to the Function
> immediately following receipt of an FRS Message indicating Configuration-Ready,
> however, this does not necessarily indicate that outstanding Requests initiated
> by the Function have completed."
> 
> 
> Kind regards,
> Niklas

We can ask our HW engineers to implement function readiness but we need to be
able to support exiting products, hence why posting it as a quirk.