linux-kernel - [PATCH v2] PCI: Coalesce contiguous regions for host bridges

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Date:   Thu,  1 Apr 2021 21:12:52 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     bhelgaas@...gle.com
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        linux-pci@...r.kernel.org (open list:PCI SUBSYSTEM),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2] PCI: Coalesce contiguous regions for host bridges

Built-in graphics on HP EliteDesk 805 G6 doesn't work because graphics
can't get the BAR it needs:
[    0.611504] pci_bus 0000:00: root bus resource [mem 0x10020200000-0x100303fffff window]
[    0.611505] pci_bus 0000:00: root bus resource [mem 0x10030400000-0x100401fffff window]
...
[    0.638083] pci 0000:00:08.1:   bridge window [mem 0xd2000000-0xd23fffff]
[    0.638086] pci 0000:00:08.1:   bridge window [mem 0x10030000000-0x100401fffff 64bit pref]
[    0.962086] pci 0000:00:08.1: can't claim BAR 15 [mem 0x10030000000-0x100401fffff 64bit pref]: no compatible bridge window
[    0.962086] pci 0000:00:08.1: [mem 0x10030000000-0x100401fffff 64bit pref] clipped to [mem 0x10030000000-0x100303fffff 64bit pref]
[    0.962086] pci 0000:00:08.1:   bridge window [mem 0x10030000000-0x100303fffff 64bit pref]
[    0.962086] pci 0000:07:00.0: can't claim BAR 0 [mem 0x10030000000-0x1003fffffff 64bit pref]: no compatible bridge window
[    0.962086] pci 0000:07:00.0: can't claim BAR 2 [mem 0x10040000000-0x100401fffff 64bit pref]: no compatible bridge window

However, the root bus has two contiguous regions that can contain the
child resource requested.

Bjorn Helgaas pointed out that we can simply coalesce contiguous regions
for host bridges, since host bridge don't have _SRS. So do that
accordingly to make child resource can be contained. This change makes
the graphics works on the system in question.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212013
Suggested-by: Bjorn Helgaas <bhelgaas@...gle.com>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
---
v2:
 - Coalesce all contiguous regresion in pci_register_host_bridge(), if
   conditions are met.

 drivers/pci/probe.c | 49 +++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 45 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 953f15abc850..3607ce7402b4 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -19,6 +19,7 @@
 #include <linux/hypervisor.h>
 #include <linux/irqdomain.h>
 #include <linux/pm_runtime.h>
+#include <linux/list_sort.h>
 #include "pci.h"
 
 #define CARDBUS_LATENCY_TIMER	176	/* secondary latency timer */
@@ -874,14 +875,30 @@ static void pci_set_bus_msi_domain(struct pci_bus *bus)
 	dev_set_msi_domain(&bus->dev, d);
 }
 
+static int res_cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+	struct resource_entry *entry1, *entry2;
+
+	entry1 = container_of(a, struct resource_entry, node);
+	entry2 = container_of(b, struct resource_entry, node);
+
+	if (entry1->res->flags != entry2->res->flags)
+		return entry1->res->flags > entry2->res->flags;
+
+	if (entry1->offset != entry2->offset)
+		return entry1->offset > entry2->offset;
+
+	return entry1->res->start > entry2->res->start;
+}
+
 static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 {
 	struct device *parent = bridge->dev.parent;
-	struct resource_entry *window, *n;
+	struct resource_entry *window, *next, *n;
 	struct pci_bus *bus, *b;
-	resource_size_t offset;
+	resource_size_t offset, next_offset;
 	LIST_HEAD(resources);
-	struct resource *res;
+	struct resource *res, *next_res;
 	char addr[64], *fmt;
 	const char *name;
 	int err;
@@ -959,11 +976,35 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	if (nr_node_ids > 1 && pcibus_to_node(bus) == NUMA_NO_NODE)
 		dev_warn(&bus->dev, "Unknown NUMA node; performance will be reduced\n");
 
+	/* Sort and coalesce contiguous windows */
+	list_sort(NULL, &resources, res_cmp);
+	resource_list_for_each_entry_safe(window, n, &resources) {
+		if (list_is_last(&window->node, &resources))
+			break;
+
+		next = list_next_entry(window, node);
+		offset = window->offset;
+		res = window->res;
+		next_offset = next->offset;
+		next_res = next->res;
+
+		if (res->flags != next_res->flags || offset != next_offset)
+			continue;
+
+		if (res->end + 1 == next_res->start) {
+			next_res->start = res->start;
+			res->flags = res->start = res->end = 0;
+		}
+	}
+
 	/* Add initial resources to the bus */
 	resource_list_for_each_entry_safe(window, n, &resources) {
-		list_move_tail(&window->node, &bridge->windows);
 		offset = window->offset;
 		res = window->res;
+		if (!res->end)
+			continue;
+
+		list_move_tail(&window->node, &bridge->windows);
 
 		if (res->flags & IORESOURCE_BUS)
 			pci_bus_insert_busn_res(bus, bus->number, res->end);
-- 
2.30.2