linux-kernel - Re: [PATCH v2] PCI: Reduce delay after FLR of Microsoft MANA devices

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Message-ID: <aDg4PE4Zbzwps71E@wunner.de>
Date: Thu, 29 May 2025 12:34:36 +0200
From: Lukas Wunner <lukas@...ner.de>
To: grwhyte@...ux.microsoft.com
Cc: 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 v2] PCI: Reduce delay after FLR of Microsoft MANA devices

On Wed, May 28, 2025 at 06:10:47PM +0000, grwhyte@...ux.microsoft.com wrote:
> Add a device-specific reset for Microsoft MANA devices with the FLR
> delay reduced from 100ms to 10ms. While this is not compliant with the pci
> spec, these devices safely complete the FLR much quicker than 100ms and
> this can be reduced to optimize certain scenarios

How often do you reset these devices that 90 msec makes a difference?
What are these "certain scenarios"?

There are already "d3hot_delay" and "d3cold_delay" members in
struct pci_dev.  I'm wondering if it would make sense to add
another one, say, "flr_delay".  That would allow other devices
to reduce or lengthen the delay without each of them having to
duplicate pcie_flr().  The code duplication makes this difficult
to maintain long-term.

Thanks,

Lukas