linux-kernel - Re: [PATCH v4] PCI/portdrv: Only disable hotplug interrupts early when needed.

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Message-ID: <Z8VuLl8Os5BrsjrE@wunner.de>
Date: Mon, 3 Mar 2025 09:54:06 +0100
From: Lukas Wunner <lukas@...ner.de>
To: Feng Tang <feng.tang@...ux.alibaba.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
	Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Liguang Zhang <zhangliguang@...ux.alibaba.com>,
	Guanghui Feng <guanghuifeng@...ux.alibaba.com>, rafael@...nel.org,
	Markus Elfring <Markus.Elfring@....de>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	ilpo.jarvinen@...ux.intel.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] PCI/portdrv: Only disable hotplug interrupts early
 when needed.

On Mon, Mar 03, 2025 at 10:36:30AM +0800, Feng Tang wrote:
> There was problem reported by firmware developers that they received
> two PCIe hotplug commands in very short intervals on an ARM server,
> which doesn't comply with PCIe spec, and broke their state machine and
> work flow. According to PCIe 6.1 spec, section 6.7.3.2, software needs
> to wait at least 1 second for the command-complete event, before
> resending the command or sending a new command.
> 
> In the failure case, the first PCIe hotplug command firmware received
> is from get_port_device_capability(), which sends command to disable
> PCIe hotplug interrupts without waiting for its completion, and the
> second command comes from pcie_enable_notification() of pciehp driver,
> which enables hotplug interrupts again.
> 
> One solution is to add the necessary delay after the first command [1],
> while Lukas proposed an optimization that if the pciehp driver will be
> loaded soon and handle the interrupts, then the hotplug and the wait
> are not needed and can be saved, for every root port.
> 
> So fix it by only disabling the hotplug interrupts when pciehp driver
> is not enabled.
> 
> [1]. https://lore.kernel.org/lkml/20250224034500.23024-1-feng.tang@linux.alibaba.com/t/#u
> 
> Fixes: 2bd50dd800b5 ("PCI: PCIe: Disable PCIe port services during port initialization")
> Suggested-by: Lukas Wunner <lukas@...ner.de>
> Signed-off-by: Feng Tang <feng.tang@...ux.alibaba.com>

Reviewed-by: Lukas Wunner <lukas@...ner.de>