[coreboot-gerrit] Change in coreboot[master]: pciexp_device: Prevent race condition with retrain link

[Youness Alaoui (Code Review)]

Youness Alaoui has uploaded a new change for review. ( https://review.coreboot.org/19556 )

Change subject: pciexp_device: Prevent race condition with retrain link
......................................................................

pciexp_device: Prevent race condition with retrain link

The PCIe specification[1] describes a race condition that
can occur when using the Retrain Link bit in the Link
Control Register.
The race condition is avoided by checking the retrain link
bit in the link status register and waiting until it is
set to 0, before initiating a new link retraining.

[1] PCI Express Base Specification Revision 3.0
    Page 633

Change-Id: I9d5840fb9a6e63838b5a4084d3bbe483f1d870ed
Signed-off-by: Youness Alaoui <youness.alaoui at puri.sm>
---
M src/device/pciexp_device.c
1 file changed, 19 insertions(+), 0 deletions(-)


  git pull ssh://review.coreboot.org:29418/coreboot refs/changes/56/19556/1

diff --git a/src/device/pciexp_device.c b/src/device/pciexp_device.c
index 0c36538..fb2a284 100644
--- a/src/device/pciexp_device.c
+++ b/src/device/pciexp_device.c
@@ -53,6 +53,25 @@
 	unsigned try = PCIE_TRAIN_RETRY;
 	u16 lnk;
 
+	/* Implementation note (page 633) in PCIe Specification 3.0 suggests
+	 * polling the Link Training bit in the Link Status register until the
+	 * value returned is 0 before setting the Retrain Link bit to 1.
+	 * This is meant to avoid a race condition when using the
+	 * Retrain Link mechanism.
+	 */
+	while (try--) {
+		lnk = pci_read_config16(dev, cap + PCI_EXP_LNKSTA);
+		if (!(lnk & PCI_EXP_LNKSTA_LT)) {
+			try = PCIE_TRAIN_RETRY;
+			break;
+		}
+		udelay(100);
+	}
+	if (try != PCIE_TRAIN_RETRY) {
+		printk(BIOS_ERR, "%s: Link Retrain timeout\n", dev_path(dev));
+		return -1;
+	}
+
 	/* Start link retraining */
 	lnk = pci_read_config16(dev, cap + PCI_EXP_LNKCTL);
 	lnk |= PCI_EXP_LNKCTL_RL;

-- 
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I9d5840fb9a6e63838b5a4084d3bbe483f1d870ed
Gerrit-PatchSet: 1
Gerrit-Project: coreboot
Gerrit-Branch: master
Gerrit-Owner: Youness Alaoui <snifikino at gmail.com>