linux-kernel - Re: [PATCH v3 06/12] x86/amd_nb: Use topology info to get AMD node count

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Message-ID: <20251023202503.72987338.michal.pecio@gmail.com>
Date: Thu, 23 Oct 2025 20:25:03 +0200
From: Michal Pecio <michal.pecio@...il.com>
To: Yazen Ghannam <yazen.ghannam@....com>
Cc: Shyam-sundar.S-k@....com, bhelgaas@...gle.com, hdegoede@...hat.com,
 ilpo.jarvinen@...ux.intel.com, jdelvare@...e.com,
 linux-edac@...r.kernel.org, linux-hwmon@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
 linux@...ck-us.net, mario.limonciello@....com,
 naveenkrishna.chatradhi@....com, platform-driver-x86@...r.kernel.org,
 suma.hegde@....com, tony.luck@...el.com, x86@...nel.org
Subject: Re: [PATCH v3 06/12] x86/amd_nb: Use topology info to get AMD node
 count

On Thu, 23 Oct 2025 12:09:06 -0400, Yazen Ghannam wrote:
> The kernel seems to think there are 6 CPUs on your system:
> 
> [    0.072059] CPU topo: Allowing 4 present CPUs plus 2 hotplug CPUs

I wonder if this code doesn't break systems which actually support
hotplug, when some sockets aren't populated at boot?


	amd_northbridges.num = amd_num_nodes();

This count apparently includes potential hotplug nodes.

	for (i = 0; i < amd_northbridges.num; i++) {
		node_to_amd_nb(i)->misc = amd_node_get_func(i, 3);

This is a wrapper around pci_get_domain_bus_and_slot(). Isn't this PCI
device part of CPU "uncore" and absent until a CPU is hotplugged?

		/*
		 * Each Northbridge must have a 'misc' device.
		 * If not, then uninitialize everything.
		 */
		if (!node_to_amd_nb(i)->misc) {

And if it's absent, all previously found northbridges are ignored.
BTW, kerneldoc seems to suggest pci_dev_put() should be here?

			amd_northbridges.num = 0;
			kfree(nb);
			return -ENODEV;
		}

		node_to_amd_nb(i)->link = amd_node_get_func(i, 4);
	}

Regards,
Michal