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

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Message-ID: <g6azpscddqx4kqnpoy3lrfsczfjnn2hev2q5qzuwdi62wmipr2@rhzi3av3n4ab>
Date: Fri, 13 Jun 2025 19:26:46 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Lukas Wunner <lukas@...ner.de>
Cc: grwhyte@...ux.microsoft.com, linux-pci@...r.kernel.org, 
	shyamsaini@...ux.microsoft.com, code@...icks.com, Okaya@...nel.org, bhelgaas@...gle.com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/2] PCI: Reduce FLR delay to 10ms for MSFT devices

On Fri, Jun 13, 2025 at 03:45:35PM +0200, Lukas Wunner wrote:
> On Fri, Jun 13, 2025 at 05:12:48PM +0530, Manivannan Sadhasivam wrote:
> > On Wed, Jun 11, 2025 at 12:05:50AM +0000, grwhyte@...ux.microsoft.com wrote:
> > > 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.
> > > 
> > 
> > I don't think it is acceptable to *reduce* the standard delay just
> > because your device completes it more quickly. Proper way to reduce
> > the timing would be to support FRS as you said, but we cannot have
> > arbitrary delays for random devices.
> 
> To be fair, we already have that for certain devices:
> 
> The quirk delay_250ms_after_flr() is referenced by three different
> Vendor ID / Device ID combos and *lengthens* the delay after FLR.
> 

This quirk is fine as it works around an issue in the device. But this patch is
not fixing/working around an issue in the device, but rather optimizing the
delay for performance, which is not what quirks are used for AFAIK.

> It's probably difficult to justify rejecting custom delays for
> certain MANA devices, even though we allowed them for three other
> devices.
> 

If the MANA devices require extended delay, then a quirk indeed makes sense.
But it is the other way around.

> The proposed patch introduces a generic solution which avoids
> further cluttering up pci_dev_reset_methods[] with extra entries,
> so I think it's an approach worth considering.
> 
> There are a bunch of nits in the proposed patches, such as "pci"
> not being capitalized, but the general approach seems fine to me.
> 

I honestly don't know if there is any other way to handle this. So I think it is
upto Bjorn to take a call.

- Mani

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