linux-kernel - [PATCH v2 1/3] PCI/PTM: Preserve PTM Root Select

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Date:   Fri,  2 Sep 2022 18:35:41 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Rajvi Jingar <rajvi.jingar@...ux.intel.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>
Cc:     Koba Ko <koba.ko@...onical.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "David E . Box" <david.e.box@...ux.intel.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: [PATCH v2 1/3] PCI/PTM: Preserve PTM Root Select

From: Bjorn Helgaas <bhelgaas@...gle.com>

When disabling PTM, there's no need to clear the Root Select bit.  We
disable PTM during suspend, and we want to re-enable it during resume.
Clearing Root Select here makes re-enabling more complicated.

Per PCIe r6.0, sec 7.9.15.3, "When set, if the PTM Enable bit is also Set,
this Time Source is the PTM Root," so if PTM Enable is cleared, the value
of Root Select should be irrelevant.

Preserve Root Select to simplify re-enabling PTM.

Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: David E. Box <david.e.box@...ux.intel.com>
---
 drivers/pci/pcie/ptm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
index 368a254e3124..b6a417247ce3 100644
--- a/drivers/pci/pcie/ptm.c
+++ b/drivers/pci/pcie/ptm.c
@@ -42,7 +42,7 @@ void pci_disable_ptm(struct pci_dev *dev)
 		return;
 
 	pci_read_config_word(dev, ptm + PCI_PTM_CTRL, &ctrl);
-	ctrl &= ~(PCI_PTM_CTRL_ENABLE | PCI_PTM_CTRL_ROOT);
+	ctrl &= ~PCI_PTM_CTRL_ENABLE;
 	pci_write_config_word(dev, ptm + PCI_PTM_CTRL, ctrl);
 }
 
-- 
2.25.1