linux-kernel - Re: [PATCH v2] PCI: Use downstream bridges for distributing resources

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Message-ID: <99a4ee84-e41d-472d-8935-8f2a2de837ec@nvidia.com>
Date: Wed, 18 Dec 2024 19:12:09 +0800
From: Kai-Heng Feng <kaihengf@...dia.com>
To: bhelgaas@...gle.com
Cc: Mika Westerberg <mika.westerberg@...ux.intel.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>,
 Chia-Lin Kao <acelan.kao@...onical.com>
Subject: Re: [PATCH v2] PCI: Use downstream bridges for distributing resources

Hi Bjorn,

On 2024/12/4 1:48 PM, Mika Westerberg wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Wed, Dec 04, 2024 at 10:24:57AM +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: Mika Westerberg <mika.westerberg@...ux.intel.com>

Is it possible to pickup this up in 6.13 window?

Kai-Heng