linux-kernel - Re: [PATCH v2] ACPI: pci_root: Clear the acpi dependencies after PCI root bridge initialization on RISC-V

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAJZ5v0iZukqD0atbdfBnmZAxUzNB6sTcJ1YUeAo5a8NRn-emEg@mail.gmail.com>
Date: Tue, 27 Jan 2026 18:50:24 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, huyuye <huyuye812@....com>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Sunil V L <sunilvl@...tanamicro.com>, 
	Paul Walmsley <pjw@...nel.org>, Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Alexandre Ghiti <alex@...ti.fr>, Robert Moore <robert.moore@...el.com>, linux-pci@...r.kernel.org, 
	linux-acpi@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, dai.hualiang@....com.cn, 
	deng.weixian@....com.cn, guo.chang2@....com.cn, liu.qingtao2@....com.cn, 
	wu.jiabao@....com.cn, lin.yongchun@....com.cn, hu.yuye@....com.cn, 
	zhang.longxiang@....com.cn, zuo.jiang@....com.cn, li.kunpeng@....com.cn
Subject: Re: [PATCH v2] ACPI: pci_root: Clear the acpi dependencies after PCI
 root bridge initialization on RISC-V

On Tue, Jan 27, 2026 at 6:26 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Tue, Jan 27, 2026 at 04:00:49PM +0100, Rafael J. Wysocki wrote:
> > On Mon, Jan 12, 2026 at 3:17 PM huyuye <huyuye812@....com> wrote:
> > >
> > > Hi Rafael,
> > > Thank you for your thorough review and valuable comments on v1.
> > > I've updated the patch as follows:
> > > 1. Removed the redundant #ifdef CONFIG_ACPI and if (!acpi_disabled)
> > > guard as you pointed out. The entire code block indeed already depends
> > > on CONFIG_ACPI at a higher level, making the inner guard unnecessary.
> > > 2. Moved acpi_dev_clear_dependencies to RISC-V specific architecture
> > > code (driver/acpi/riscv/acpi_pci.c). This ensures that ACPI dependency
> > > clearing is handled within the appropriate architectural context.
> > >
> > > Best regards
> > > Signed-off-by: huyuye <huyuye812@....com>
> > > ---
> > >  drivers/acpi/pci_root.c       |  6 ++++++
> > >  drivers/acpi/riscv/Makefile   |  2 +-
> > >  drivers/acpi/riscv/acpi_pci.c | 11 +++++++++++
> > >  include/acpi/acpi_bus.h       |  1 +
> > >  4 files changed, 19 insertions(+), 1 deletion(-)
> > >  create mode 100644 drivers/acpi/riscv/acpi_pci.c
> > >
> > > diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> > > index 9d7f85dadc48..a16eb9097cdc 100644
> > > --- a/drivers/acpi/pci_root.c
> > > +++ b/drivers/acpi/pci_root.c
> > > @@ -30,6 +30,11 @@ static int acpi_pci_root_add(struct acpi_device *device,
> > >                              const struct acpi_device_id *not_used);
> > >  static void acpi_pci_root_remove(struct acpi_device *device);
> > >
> > > +
> > > +void __weak arch_acpi_pci_root_add_clear_dep(struct acpi_device *device)
> > > +{
> > > +}
> > > +
> > >  static int acpi_pci_root_scan_dependent(struct acpi_device *adev)
> > >  {
> > >         acpiphp_check_host_bridge(adev);
> > > @@ -760,6 +765,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
> > >         pci_lock_rescan_remove();
> > >         pci_bus_add_devices(root->bus);
> > >         pci_unlock_rescan_remove();
> > > +       arch_acpi_pci_root_add_clear_dep(device);
> >
> > Actually, this could be as simple as
> >
> >        if (IS_ENABLED(CONFIG_RISCV))
> >               acpi_dev_clear_dependencies(device);
> >
> > with a brief comment explaining why it is needed.
> >
> > Bjorn, any thoughts?
>
> The justification ("If a host bridge B depends on host bridge A (via
> _DEP), this call allows bridge B to proceed with enumeration after
> bridge A is fully initialized") doesn't sound specific to RISC-V.

But there are no _DEP dependencies between host bridgers on other
architectures in practice.

acpi_dev_clear_dependencies() could be called unconditionally here,
but it would be useless overhead if no such dependencies existed.

> For that matter, it doesn't sound specific to host bridges either.

No, it is not specific to host bridges.

> The _DEP spec language is a bit vague.  ACPI r6.6, sec 6.5.8, says:
>
>   _DEP evaluates to a package and designates device objects that OSPM
>   should assign a higher priority in start ordering due to
>   dependencies between devices (for example, related to future
>   operation region accesses).
>
> I don't know what "device start" means.  It sounds like this alludes
> to the order in which OSPM runs some device start method?  _INI?
> Should acpi_dev_clear_dependencies() be done at the point where that
> device start method is run?

Not really.

acpi_dev_clear_dependencies() is related to the way Linux uses _DEP
which is to defer the enumeration of dependent devices until the
devices they depend on are ready.

So by calling acpi_dev_clear_dependencies() the driver basically
allows other drivers to bind to devices.