linux-kernel - pci 0000:00:07.0: DPC: RP PIO log size 0 is invalid

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Date:   Mon, 7 Dec 2020 14:08:00 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Mario Limonciello <mario.limonciello@...l.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: pci 0000:00:07.0: DPC: RP PIO log size 0 is invalid

[Bringing the issue up on the list in case the Linux Bugzilla is not 
monitored/used.]


Dear Linux folks,


On Intel Tiger Lake Dell laptop, Linux logs the error below [1].

     [    0.507307] pci 0000:00:07.0: DPC: RP PIO log size 0 is invalid
     [    0.508835] pci 0000:00:07.2: DPC: RP PIO log size 0 is invalid

     $ lspci -nn -s 00:07
     00:07.0 PCI bridge [0604]: Intel Corporation Tiger Lake-LP 
Thunderbolt PCI Express Root Port #0 [8086:9a23] (rev 01)
     00:07.2 PCI bridge [0604]: Intel Corporation Tiger Lake-LP 
Thunderbolt PCI Express Root Port #2 [8086:9a27] (rev 01)

Commit 2700561817 (PCI/DPC: Cache DPC capabilities in 
pci_init_capabilities()) [1] probably introduced it in Linux 5.7.

What does this error actually mean?

	pdev->dpc_rp_log_size = (cap & PCI_EXP_DPC_RP_PIO_LOG_SIZE) >> 8;
	if (pdev->dpc_rp_log_size < 4 || pdev->dpc_rp_log_size > 9) {
		pci_err(pdev, "RP PIO log size %u is invalid\n",
			pdev->dpc_rp_log_size);
		pdev->dpc_rp_log_size = 0;
	}

(I guess `cap & PCI_EXP_DPC_RP_PIO_LOG_SIZE` is zero too?)

Is it a firmware issue or a hardware issue?


Kind regards,

Paul


[1]: https://bugzilla.kernel.org/show_bug.cgi?id=209943
      "pci 0000:00:07.0: DPC: RP PIO log size 0 is invalid"
[2]: 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=27005618178ef9e9bf9c42fd91101771c92e9308