linux-kernel - [PATCH] PCI: pciehp: Optimize PCIe root resume time

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Message-Id: <1481323406-12865-1-git-send-email-vaibhav.shankar@intel.com>
Date:   Fri,  9 Dec 2016 14:43:26 -0800
From:   Vaibhav Shankar <vaibhav.shankar@...el.com>
To:     bhelgaas@...gle.com, vaibhav.shankar@...el.com
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        venkateswarlu.v.vinjamuri@...el.com
Subject: [PATCH] PCI: pciehp: Optimize PCIe root resume time

On Apollolake platforms, PCIe rootport takes a long time to resume
from S3. With 100ms delay before read pci conf, rootport takes
~200ms during resume.

commit 2f5d8e4ff947 ("PCI: pciehp: replace unconditional sleep with
config space access check") is the one that added the 100ms delay
before reading pci conf.

This patch removes the 100ms delay.By removing the delay, the
PCIe root port takes ~16ms during resume. As per PCIe spec, we
only require 1000ms delay. This delay is provide by
pci_bus_check_dev() function.

With 100ms delay:
[  155.102713] calling  0000:00:14.0+ @ 70, parent: pci0000:00, cb: pci_pm_resume_noirq
[  155.119337] call 0000:00:14.0+ returned 0 after 16231 usecs
[  155.119467] calling  0000:01:00.0+ @ 5845, parent: 0000:00:14.0, cb: pci_pm_resume_noirq
[  155.321670] call 0000:00:14.0+ returned 0 after 185327 usecs
[  155.321743] calling  0000:01:00.0+ @ 5849, parent: 0000:00:14.0, cb: pci_pm_resume

After removing 100ms delay:
[   36.624709] calling  0000:00:14.0+ @ 4434, parent: pci0000:00, cb: pci_pm_resume_noirq
[   36.641367] call 0000:00:14.0+ returned 0 after 16263 usecs
[   36.652458] calling  0000:00:14.0+ @ 4443, parent: pci0000:00, cb: pci_pm_resume
[   36.652673] call 0000:00:14.0+ returned 0 after 208 usecs
[   36.652863] calling  0000:01:00.0+ @ 4442, parent: 0000:00:14.0, cb: pci_pm_resume

Signed-off-by: Vaibhav Shankar <vaibhav.shankar@...el.com>
---
 drivers/pci/hotplug/pciehp_hpc.c |    2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index 5c24e93..08357e7 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -311,8 +311,6 @@ int pciehp_check_link_status(struct controller *ctrl)
 	else
 		msleep(1000);
 
-	/* wait 100ms before read pci conf, and try in 1s */
-	msleep(100);
 	found = pci_bus_check_dev(ctrl->pcie->port->subordinate,
 					PCI_DEVFN(0, 0));
 
-- 
1.7.9.5