Re: [PATCH] PCI: Use downstream bridges for distributing resources

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Thu, Nov 28, 2024 at 04:40:39PM +0800, Kai-Heng Feng wrote:
> 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@nvidia.com>
> Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: Chris Chiu <chris.chiu@canonical.com>
> Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
> Reviewed-by: Matthew R. Ochs <mochs@nvidia.com>
> Reviewed-by: Koba Ko <kobak@nvidia.com>
> Fixes: 7180c1d08639 ("PCI: Distribute available resources for root buses, too")
> Signed-off-by: Kai-Heng Feng <kaihengf@nvidia.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 bukjijs.
>  		 */
>  		if (bridge && pci_bridge_resources_not_assigned(dev))
> -			pci_bridge_distribute_available_resources(bridge,
> +			pci_bridge_distribute_available_resources(dev,
>  								  add_list);

I think it looks better if you put this into one line instead:

			pci_bridge_distribute_available_resources(dev, add_list);


Otherwise looks good. I wonder if you checked that this still works with
the cases 7180c1d08639 tried to solve? ;-)
>  		else
>  			pci_root_bus_distribute_available_resources(b, add_list);
> -- 
> 2.47.0