From cfc0028627cadfa271fab0290f18731193d63d87 Mon Sep 17 00:00:00 2001
From: Bjorn Helgaas <bhelgaas@google.com>
Date: Tue, 4 Oct 2022 21:58:08 -0500
Subject: [PATCH] PCI/ASPM: Ignore L1 PM Substates if device lacks capability
Git-commit: cfc0028627cadfa271fab0290f18731193d63d87
Patch-mainline: v6.1-rc1
References: git-fixes

187f91db8237 ("PCI/ASPM: Remove struct aspm_register_info.l1ss_cap")
inadvertently removed a check for existence of the L1 PM Substates (L1SS)
Capability before reading it.

If there is no L1SS Capability, this means we mistakenly read PCI_COMMAND
and PCI_STATUS (config address 0x04) and interpret that as the PCI_L1SS_CAP
register, so we may incorrectly configure L1SS.

Make sure the L1SS Capability exists before trying to read it.

Fixes: 187f91db8237 ("PCI/ASPM: Remove struct aspm_register_info.l1ss_cap")
Link: https://lore.kernel.org/r/20221005025809.2247547-3-helgaas@kernel.org
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/pci/pcie/aspm.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -605,6 +605,9 @@ static void pcie_aspm_cap_init(struct pc
 	link->latency_up.l1 = calc_l1_latency(parent_lnkcap);
 	link->latency_dw.l1 = calc_l1_latency(child_lnkcap);
 
+	if (!parent->l1ss || !child->l1ss)
+		return;
+
 	/* Setup L1 substate */
 	pci_read_config_dword(parent, parent->l1ss + PCI_L1SS_CAP,
 			      &parent_l1ss_cap);