linux-kernel - Re: [PATCH 1/1] PCI: Wait for Link before restoring Downstream Buses

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Message-ID: <20240809203621.GA214516@bhelgaas>
Date: Fri, 9 Aug 2024 15:36:21 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: "David E . Box" <david.e.box@...ux.intel.com>,
	Jian-Hong Pan <jhp@...lessos.org>, Lukas Wunner <lukas@...ner.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 1/1] PCI: Wait for Link before restoring Downstream Buses

On Thu, Aug 08, 2024 at 03:17:07PM +0300, Ilpo Järvinen wrote:
> __pci_reset_bus() calls pci_bridge_secondary_bus_reset() to perform the
> reset and also waits for the Secondary Bus to become again accessible.
> __pci_reset_bus() then calls pci_bus_restore_locked() that restores the
> PCI devices connected to the bus, and if necessary, recursively restores
> also the subordinate buses and their devices.
> 
> The logic in pci_bus_restore_locked() does not take into account that
> after restoring a device on one level, there might be another Link
> Downstream that can only start to come up after restore has been
> performed for its Downstream Port device. That is, the Link may
> require additional wait until it becomes accessible.
> 
> Similarly, pci_slot_restore_locked() lacks wait.
> 
> Amend pci_bus_restore_locked() and pci_slot_restore_locked() to wait
> for the Secondary Bus before recursively performing the restore of that
> bus.
> 
> Fixes: 090a3c5322e9 ("PCI: Add pci_reset_slot() and pci_reset_bus()")
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

Seems reasonable to me, applied to pci/reset for v6.12, thanks!

> ---
> 
> NOTE TO MAINTAINER: I've not seen anything to actually trigger this issue
> but only realized this problem exist while looking into the other issues
> related to bus reset/restore. The fix regardless seems to make sense so
> sending it out.
> 
>  drivers/pci/pci.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index e3a49f66982d..98c7b732998a 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5671,8 +5671,10 @@ static void pci_bus_restore_locked(struct pci_bus *bus)
>  
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
>  		pci_dev_restore(dev);
> -		if (dev->subordinate)
> +		if (dev->subordinate) {
> +			pci_bridge_wait_for_secondary_bus(dev, "bus reset");
>  			pci_bus_restore_locked(dev->subordinate);
> +		}
>  	}
>  }
>  
> @@ -5706,8 +5708,10 @@ static void pci_slot_restore_locked(struct pci_slot *slot)
>  		if (!dev->slot || dev->slot != slot)
>  			continue;
>  		pci_dev_restore(dev);
> -		if (dev->subordinate)
> +		if (dev->subordinate) {
> +			pci_bridge_wait_for_secondary_bus(dev, "slot reset");
>  			pci_bus_restore_locked(dev->subordinate);
> +		}
>  	}
>  }
>  
> -- 
> 2.39.2
>