linux-kernel - [PATCH] PCI: Use downstream bridges for distributing resources

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Message-Id: <20241128084039.54972-1-kaihengf@nvidia.com>
Date: Thu, 28 Nov 2024 16:40:39 +0800
From: Kai-Heng Feng <kaihengf@...dia.com>
To: bhelgaas@...gle.com,
	mika.westerberg@...ux.intel.com
Cc: linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Kai-Heng Feng <kaihengf@...dia.com>,
	Carol Soto <csoto@...dia.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Chris Chiu <chris.chiu@...onical.com>,
	"Matthew R . Ochs" <mochs@...dia.com>,
	Koba Ko <kobak@...dia.com>
Subject: [PATCH] PCI: Use downstream bridges for distributing resources

Commit 7180c1d08639 ("PCI: Distribute available resources for root
buses, too") breaks BAR assignment on some devcies:
[   10.021193] pci 0006:03:00.0: BAR 0 [mem 0x6300c0000000-0x6300c1ffffff 64bit pref]: assigned
[   10.029880] pci 0006:03:00.1: BAR 0 [mem 0x6300c2000000-0x6300c3ffffff 64bit pref]: assigned
[   10.038561] pci 0006:03:00.2: BAR 0 [mem size 0x00800000 64bit pref]: can't assign; no space
[   10.047191] pci 0006:03:00.2: BAR 0 [mem size 0x00800000 64bit pref]: failed to assign
[   10.055285] pci 0006:03:00.0: VF BAR 0 [mem size 0x02000000 64bit pref]: can't assign; no space
[   10.064180] pci 0006:03:00.0: VF BAR 0 [mem size 0x02000000 64bit pref]: failed to assign
[   10.072543] pci 0006:03:00.1: VF BAR 0 [mem size 0x02000000 64bit pref]: can't assign; no space
[   10.081437] pci 0006:03:00.1: VF BAR 0 [mem size 0x02000000 64bit pref]: failed to assign

The apertures of domain 0006 before the commit:
6300c0000000-63ffffffffff : PCI Bus 0006:00
  6300c0000000-6300c9ffffff : PCI Bus 0006:01
    6300c0000000-6300c9ffffff : PCI Bus 0006:02
      6300c0000000-6300c8ffffff : PCI Bus 0006:03
        6300c0000000-6300c1ffffff : 0006:03:00.0
          6300c0000000-6300c1ffffff : mlx5_core
        6300c2000000-6300c3ffffff : 0006:03:00.1
          6300c2000000-6300c3ffffff : mlx5_core
        6300c4000000-6300c47fffff : 0006:03:00.2
        6300c4800000-6300c67fffff : 0006:03:00.0
        6300c6800000-6300c87fffff : 0006:03:00.1
      6300c9000000-6300c9bfffff : PCI Bus 0006:04
        6300c9000000-6300c9bfffff : PCI Bus 0006:05
          6300c9000000-6300c91fffff : PCI Bus 0006:06
          6300c9200000-6300c93fffff : PCI Bus 0006:07
          6300c9400000-6300c95fffff : PCI Bus 0006:08
          6300c9600000-6300c97fffff : PCI Bus 0006:09

After the commit:
6300c0000000-63ffffffffff : PCI Bus 0006:00
  6300c0000000-6300c9ffffff : PCI Bus 0006:01
    6300c0000000-6300c9ffffff : PCI Bus 0006:02
      6300c0000000-6300c43fffff : PCI Bus 0006:03
        6300c0000000-6300c1ffffff : 0006:03:00.0
          6300c0000000-6300c1ffffff : mlx5_core
        6300c2000000-6300c3ffffff : 0006:03:00.1
          6300c2000000-6300c3ffffff : mlx5_core
      6300c4400000-6300c4dfffff : PCI Bus 0006:04
        6300c4400000-6300c4dfffff : PCI Bus 0006:05
          6300c4400000-6300c45fffff : PCI Bus 0006:06
          6300c4600000-6300c47fffff : PCI Bus 0006:07
          6300c4800000-6300c49fffff : PCI Bus 0006:08
          6300c4a00000-6300c4bfffff : PCI Bus 0006:09

We can see that the window of 0006:03 gets shrunken too much and 0006:04
eats away the window for 0006:03:00.2.

The offending commit distributes the upstream bridge's resources
multiple times to every downstream bridges, hence makes the aperture
smaller than desired because calculation of io_per_b, mmio_per_b and
mmio_pref_per_b becomes incorrect.

Instead, distributing downstream bridges' own resources to resolve the
issue.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=219540
Cc: Carol Soto <csoto@...dia.com>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: Chris Chiu <chris.chiu@...onical.com>
Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>
Reviewed-by: Matthew R. Ochs <mochs@...dia.com>
Reviewed-by: Koba Ko <kobak@...dia.com>
Fixes: 7180c1d08639 ("PCI: Distribute available resources for root buses, too")
Signed-off-by: Kai-Heng Feng <kaihengf@...dia.com>
---
 drivers/pci/setup-bus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 23082bc0ca37..2db19c17e824 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -2105,7 +2105,7 @@ pci_root_bus_distribute_available_resources(struct pci_bus *bus,
 		 * in case of root bus.
 		 */
 		if (bridge && pci_bridge_resources_not_assigned(dev))
-			pci_bridge_distribute_available_resources(bridge,
+			pci_bridge_distribute_available_resources(dev,
 								  add_list);
 		else
 			pci_root_bus_distribute_available_resources(b, add_list);
-- 
2.47.0