linux-kernel - [PATCH V2] PCI/ASPM: reconfigure ASPM following hotplug for POLICY

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Date:   Tue, 31 Jan 2017 14:45:27 -0500
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-pci@...r.kernel.org, timur@...eaurora.org, cov@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sinan Kaya <okaya@...eaurora.org>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH V2] PCI/ASPM: reconfigure ASPM following hotplug for POLICY_DEFAULT

When the operating system is booted with the default ASPM policy
(POLICY_DEFAULT), the current code is determining the ASPM policy
set up by the BIOS by querying the enable/disable states from ASPM
registers.

In the case of hotplug removal, the ASPM registers get cleared by
calling the pcie_aspm_exit_link_state() function.

An insertion following hotplug removal reads incorrect policy as
ASPM disabled even though ASPM was enabled during boot.

Adding a flag to the struct pci_dev and saving the power up policy
in the bridge to be reused during hotplug insertion. Bridge's enable
counter is used as a switch to determine when to use saved value.

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 drivers/pci/pcie/aspm.c | 21 +++++++++++++++++----
 include/linux/pci.h     |  1 +
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 17ac1dc..5cfcc6d 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -338,8 +338,9 @@ static void pcie_aspm_check_latency(struct pci_dev *endpoint)
 	}
 }
 
-static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
+static void pcie_aspm_cap_init(struct pci_dev *pdev, int blacklist)
 {
+	struct pcie_link_state *link = pdev->link_state;
 	struct pci_dev *child, *parent = link->pdev;
 	struct pci_bus *linkbus = parent->subordinate;
 	struct aspm_register_info upreg, dwreg;
@@ -397,8 +398,20 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 	link->latency_up.l1 = calc_l1_latency(upreg.latency_encoding_l1);
 	link->latency_dw.l1 = calc_l1_latency(dwreg.latency_encoding_l1);
 
-	/* Save default state */
-	link->aspm_default = link->aspm_enabled;
+	/*
+	 * Save default state from FW when enabling ASPM for the first time
+	 * during boot by looking at the calculated link->aspm_enabled bits
+	 * above and enable_cnt will be zero.
+	 *
+	 * If this path is getting called for the second/third time
+	 * (enable_cnt will be non-zero). Assume that the current state of the
+	 * ASPM registers may not necessarily match what FW asked us to do as
+	 * in the case of hotplug insertion/removal.
+	 */
+	if (!atomic_read(&pdev->enable_cnt))
+		pdev->aspm_default = link->aspm_default = link->aspm_enabled;
+	else
+		link->aspm_default = pdev->aspm_default;
 
 	/* Setup initial capable state. Will be updated later */
 	link->aspm_capable = link->aspm_support;
@@ -599,7 +612,7 @@ void pcie_aspm_init_link_state(struct pci_dev *pdev)
 	 * upstream links also because capable state of them can be
 	 * update through pcie_aspm_cap_init().
 	 */
-	pcie_aspm_cap_init(link, blacklist);
+	pcie_aspm_cap_init(pdev, blacklist);
 
 	/* Setup initial Clock PM state */
 	pcie_clkpm_cap_init(link, blacklist);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index e2d1a12..521f88c 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -321,6 +321,7 @@ struct pci_dev {
 
 #ifdef CONFIG_PCIEASPM
 	struct pcie_link_state	*link_state;	/* ASPM link state */
+	unsigned int	aspm_default;		/* ASPM policy set by BIOS */
 #endif
 
 	pci_channel_state_t error_state;	/* current connectivity state */
-- 
1.9.1