Message-ID: <4a88159f-b0f7-43ae-b379-d64c25f417bb@nvidia.com>
Date: Thu, 28 Nov 2024 19:11:31 +0800
From: Kai-Heng Feng <kaihengf@...dia.com>
To: Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc: bhelgaas@...gle.com, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org, 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: Re: [PATCH] PCI: Use downstream bridges for distributing resources



On 2024/11/28 5:45 PM, Mika Westerberg wrote:
> External email: Use caution opening links or attachments
> 
> 
> 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@...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 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);

Sure, will do.

> 
> 
> Otherwise looks good. I wonder if you checked that this still works with
> the cases 7180c1d08639 tried to solve? ;-)

That's why Chris is Cc'ed.
Chris, is it possible to give this patch a try to make sure this doesn't break 
what 7180c1d08639 solved?

Will send v2 after your test result.

Kai-Heng

>>                else
>>                        pci_root_bus_distribute_available_resources(b, add_list);
>> --
>> 2.47.0

Powered by blists - more mailing lists