linux-kernel - [PATCH] PCI/ASPM: Wait for data link active after retraining

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Date:   Thu, 02 Jun 2022 06:55:44 +0000
From:   Nathan Rossi <nathan@...hanrossi.com>
To:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Nathan Rossi <nathan@...hanrossi.com>,
        Nathan Rossi <nathan.rossi@...i.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: [PATCH] PCI/ASPM: Wait for data link active after retraining

From: Nathan Rossi <nathan.rossi@...i.com>

When retraining the link either the child or the parent device may have
the data link layer state machine of the respective devices move out of
the active state despite the physical link training being completed.
Depending on how long is takes for the devices to return to the active
state, the device may not be ready and any further reads/writes to the
device can fail.

This issue is present with the pci-mvebu controller paired with a device
supporting ASPM but without advertising the Slot Clock, where during
boot the pcie_aspm_cap_init call would cause common clocks to be made
consistent and then retrain the link. However the data link layer would
not be active before any device initialization (e.g. ASPM capability
queries, BAR configuration) causing improper configuration of the device
without error.

To ensure the child device is accessible, after the link retraining use
pcie_wait_for_link to perform the associated state checks and any needed
delays.

Signed-off-by: Nathan Rossi <nathan.rossi@...i.com>
---
 drivers/pci/pcie/aspm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index a96b7424c9..4b8a1810be 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -288,7 +288,8 @@ static void pcie_aspm_configure_common_clock(struct pcie_link_state *link)
 		reg16 &= ~PCI_EXP_LNKCTL_CCC;
 	pcie_capability_write_word(parent, PCI_EXP_LNKCTL, reg16);

-	if (pcie_retrain_link(link))
+	/* Retrain link and then wait for the link to become active */
+	if (pcie_retrain_link(link) && pcie_wait_for_link(parent, true))
 		return;

 	/* Training failed. Restore common clock configurations */
---
2.36.1