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

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Message-ID: <kl2wzk5gwhp3s35cznsyelmkep2ch3rm6gbhsh3oehq4ojmbe6@zte6xclilmfv>
Date: Tue, 3 Dec 2024 14:07:23 +0800
From: "Chia-Lin Kao (AceLan)" <acelan.kao@...onical.com>
To: Kai-Heng Feng <kaihengf@...dia.com>
Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>, 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 Thu, Nov 28, 2024 at 07:11:31PM +0800, Kai-Heng Feng wrote:
> 
> 
> 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?
Verified this fix doesn't break 7180c1d08639.
DUT <-TBT-> Dock <-TBT-> storage hotplug works
DUT <-TBT-> Dock <-TBT-> monitor <-TBT-> storage hotplug works

Tested-by: Chia-Lin Kao (AceLan) <acelan.kao@...onical.com>

> 
> Will send v2 after your test result.
> 
> Kai-Heng
> 
> > >                else
> > >                        pci_root_bus_distribute_available_resources(b, add_list);
> > > --
> > > 2.47.0
>