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From:   Bjorn Helgaas <helgaas@kernel.org>
To:     linux-pci@vger.kernel.org
Cc:     Vidya Sagar <vidyas@nvidia.com>,
        "Saheed O . Bolarinwa" <refactormyself@gmail.com>,
        Lorenzo Pieralisi <lpieralisi@kernel.org>,
        =?UTF-8?q?Krzysztof=20Wilczy=C5=84ski?= <kw@linux.com>,
        Rajat Jain <rajatja@google.com>,
        "Kenneth R . Crudup" <kenny@panix.com>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>,
        Abhishek Sahu <abhsahu@nvidia.com>,
        Thierry Reding <treding@nvidia.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Krishna Thota <kthota@nvidia.com>,
        Manikanta Maddireddy <mmaddireddy@nvidia.com>,
        Vidya Sagar <sagar.tv@gmail.com>, sagupta@nvidia.com,
        linux-kernel@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>
Subject: [PATCH 2/3] PCI/ASPM: Ignore L1 PM Substates if device lacks capability
Date:   Tue,  4 Oct 2022 21:58:08 -0500
Message-Id: <20221005025809.2247547-3-helgaas@kernel.org>
In-Reply-To: <20221005025809.2247547-1-helgaas@kernel.org>
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From: Bjorn Helgaas <bhelgaas@google.com>

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")
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/pcie/aspm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 4535228e4a64..f12d117f44e0 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -560,6 +560,9 @@ static void aspm_l1ss_init(struct pcie_link_state *link)
 	u32 parent_l1ss_cap, child_l1ss_cap;
 	u32 parent_l1ss_ctl1 = 0, child_l1ss_ctl1 = 0;
 
+	if (!parent->l1ss || !child->l1ss)
+		return;
+
 	/* Setup L1 substate */
 	pci_read_config_dword(parent, parent->l1ss + PCI_L1SS_CAP,
 			      &parent_l1ss_cap);
-- 
2.25.1