linux-kernel - [PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary

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Message-ID: <20250524185304.26698-2-manivannan.sadhasivam@linaro.org>
Date: Sun, 25 May 2025 00:23:03 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: bhelgaas@...gle.com,
	lpieralisi@...nel.org,
	kw@...ux.com
Cc: linux-pci@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	cassel@...nel.org,
	wilfred.mallawa@....com,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Lukas Wunner <lukas@...ner.de>
Subject: [PATCH 1/2] PCI: Save and restore root port config space in pcibios_reset_secondary_bus()

host_bridge::reset_slot() is supposed to reset the PCI root port/slot. Once
that happens, the config space content would be lost. This was reported by
Niklas on the dw-rockchip based platform where the MPS setting of the root
port was lost after the host_bridge::reset_slot() callback. Hence, save the
config space before calling the host_bridge::reset_slot() callback and
restore it afterwards.

While at it, make sure that the callback is only called for root ports by
checking if the bridge is behind the root bus.

Fixes: d5c1e1c25b37 ("PCI/ERR: Add support for resetting the slots in a platform specific way")
Reported-by: Niklas Cassel <cassel@...nel.org>
Closes: https://lore.kernel.org/linux-pci/aC9OrPAfpzB_A4K2@ryzen
Suggested-by: Lukas Wunner <lukas@...ner.de>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
---
 drivers/pci/pci.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 4d396bbab4a8..6d6e9ce2bbcc 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4985,10 +4985,19 @@ void __weak pcibios_reset_secondary_bus(struct pci_dev *dev)
 	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
 	int ret;
 
-	if (host->reset_slot) {
+	if (pci_is_root_bus(dev->bus) && host->reset_slot) {
+		/*
+		 * Save the config space of the root port before doing the
+		 * reset, since the state could be lost. The device state
+		 * should've been saved by the caller.
+		 */
+		pci_save_state(dev);
 		ret = host->reset_slot(host, dev);
 		if (ret)
 			pci_err(dev, "failed to reset slot: %d\n", ret);
+		else
+			/* Now restore it on success */
+			pci_restore_state(dev);
 
 		return;
 	}
-- 
2.43.0