linux-kernel - [PATCH 2/2] PCI: add CRS support to error handling path

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Message-Id: <1472770801-30671-2-git-send-email-okaya@codeaurora.org>
Date:   Thu,  1 Sep 2016 19:00:01 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-pci@...r.kernel.org, timur@...eaurora.org,
        cov@...eaurora.org, alex.williamson@...hat.com,
        vikrams@...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
Subject: [PATCH 2/2] PCI: add CRS support to error handling path

The PCIE spec allows an endpoint device to extend the initialization time
beyond 1 second by issuing Configuration Request Retry Status (CRS) for a
vendor ID read request.

This basically means "I'm busy now, please call me back later".

There are two moving parts to CRS support from the SW perspective. One part
is to determine if CRS is supported or not. The second part is to set the
CRS visibility register.

As part of the probe, the Linux kernel sets the above two conditions in
pci_enable_crs function. The kernel is also honoring the returned CRS in
pci_bus_read_dev_vendor_id function if supported. The function will poll up
to specified amount of time while endpoint is returning CRS response.

The PCIe spec also allows CRS to be issued during cold, warm, hot and FLR
resets.

The hot reset is initiated by starting a secondary bus reset. This patch is
adding vendor ID read immediately after a bus reset so that the
initialization procedure can be extended by the amount of time endpoint
requires.

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 drivers/pci/pci.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b209378..ebd0fc6 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3829,6 +3829,44 @@ static int pci_pm_reset(struct pci_dev *dev, int probe)
 	return 0;
 }

+/*
+ * Mostly copy paste from pci_walk_bus with the exceptions of hard coded
+ * work and removed locks.
+ */
+static void pci_bus_probe_crs(struct pci_bus *top)
+{
+	struct pci_dev *dev;
+	struct pci_bus *bus;
+	struct list_head *next;
+	int retval;
+	u32 l;
+
+	bus = top;
+	next = top->devices.next;
+	for (;;) {
+		if (next == &bus->devices) {
+			/* end of this bus, go up or finish */
+			if (bus == top)
+				break;
+			next = bus->self->bus_list.next;
+			bus = bus->self->bus;
+			continue;
+		}
+		dev = list_entry(next, struct pci_dev, bus_list);
+		if (dev->subordinate) {
+			/* this is a pci-pci bridge, do its devices next */
+			next = dev->subordinate->devices.next;
+			bus = dev->subordinate;
+		} else
+			next = dev->bus_list.next;
+
+		retval = pci_bus_read_dev_vendor_id(dev->bus, dev->devfn, &l,
+						    60 * 1000);
+		if (retval)
+			break;
+	}
+}
+
 void pci_reset_secondary_bus(struct pci_dev *dev)
 {
 	u16 ctrl;
@@ -4361,6 +4399,7 @@ void pci_reset_bridge_secondary_bus(struct pci_dev *dev)
 	pci_bus_save_and_disable(dev->bus);
 	pcibios_reset_secondary_bus(dev);
 	pci_bus_restore(dev->bus);
+	pci_bus_probe_crs(dev->subordinate);
 }
 EXPORT_SYMBOL_GPL(pci_reset_bridge_secondary_bus);

-- 
1.9.1