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Date: Thu, 10 Sep 2026 18:51:26 -0500
From: Bjorn Helgaas <helgaas@kernel.org>
To: David Matlack <dmatlack@google.com>
Cc: kexec@lists.infradead.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
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	Adithya Jayachandran <ajayachandra@nvidia.com>,
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	Vipin Sharma <vipinsh@google.com>, William Tu <witu@nvidia.com>,
	Yi Liu <yi.l.liu@intel.com>
Subject: Re: [PATCH v8 06/12] PCI: liveupdate: Auto-preserve upstream bridges
 across Live Update
Message-ID: <20260910235126.GA367952@bhelgaas>
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In-Reply-To: <20260728221007.2098560-7-dmatlack@google.com>

On Tue, Jul 28, 2026 at 10:10:00PM +0000, David Matlack wrote:
> When a PCI device is preserved across a Live Update, all of its upstream
> bridges up to the root port must also be preserved. This enables the PCI
> core and any drivers bound to the bridges to manage bridges correctly
> across a Live Update.
> 
> Notably, this will be used in subsequent commits to ensure that
> preserved devices can continue performing memory transactions without a
> disruption or change in routing.
> 
> To preserve bridges, the PCI core tracks the number of downstream
> devices preserved under each bridge using a reference count in struct
> pci_dev_ser. This allows a bridge to remain preserved until all its
> downstream preserved devices are unpreserved or finish their
> participation in the Live Update.

This seems to hint that we're going to allow bridge reconfiguration in
some cases, e.g., for hot-adds.  The simplest case is "leave config of
all bridges the same", and I thought that was what the previous patch
commit log said.

What's the benefit added by this patch?