From: Guenter Roeck <linux@roeck-us.net>
To: Jihong Min <hurryman2212@icloud.com>
Cc: sashiko-reviews@lists.linux.dev,
Jihong Min <hurryman2212@gmail.com>,
linux-hwmon@vger.kernel.org, linux-pci@vger.kernel.org
Subject: Re: [PATCH v5 1/2] usb: xhci-pci: add AMD Promontory 21 PCI glue
Date: Thu, 14 May 2026 12:22:31 -0700 [thread overview]
Message-ID: <8cbf1ac3-bba5-4223-8425-62aa49508c63@roeck-us.net> (raw)
In-Reply-To: <1173f5c5-a740-4458-8e08-2c427a704207@icloud.com>
On Thu, May 14, 2026 at 11:29:36PM +0900, Jihong Min wrote:
>
> On 5/14/26 10:20, Guenter Roeck wrote:
> > > > + prom21_auxdev->auxdev =
> > > > + auxiliary_device_create(&pdev->dev, KBUILD_MODNAME, "hwmon",
> > > > + &prom21_auxdev->pdata,
> > > > + (pci_domain_nr(pdev->bus) << 16) |
> > > > + pci_dev_id(pdev));
> > >
> > > Does left-shifting pci_domain_nr() introduce a signed integer overflow
> > > regression?
> > >
> > > The function pci_domain_nr() returns a signed int, which can be up
> > > to 0xFFFF
> > > on ACPI systems. Left-shifting a value of 0x8000 or greater by 16 bits
> > > alters the sign bit of a 32-bit int, resulting in undefined behavior
> > > in C.
> > >
> > > Would casting the return value to an unsigned integer, such as
> > > (u32)pci_domain_nr(pdev->bus) << 16, avoid this overflow?
> > >
> > FWIW, I don't think that is a real problem. auxiliary_device_create()
> > takes an int as id parameter, so the result would be converted back to
> > int
> > anyway. Maybe use "(pci_domain_nr(pdev->bus) & 0x7fff) << 16" instead,
> > but I don't know if that adds any practical value.
> >
> > Thanks,
> > Guenter
> >
> For the auxiliary device id issue, after thinking about it a bit more, I
> think
> a simpler approach is to avoid encoding the PCI domain/BDF into the
> auxiliary
> id. The auxiliary id only needs to make the auxiliary device name unique;
> userspace identification is already tied to the parent PCI function.
>
> So instead of:
>
> (pci_domain_nr(pdev->bus) << 16) | pci_dev_id(pdev)
>
> I plan to use an IDA-allocated id:
>
> id = ida_alloc(&prom21_xhci_auxdev_ida, GFP_KERNEL);
> auxiliary_device_create(..., id);
> ida_free(&prom21_xhci_auxdev_ida, id);
Other drivers only call ida_free after the auxiliary device has been released.
Guenter
>
> This avoids both the signed shift concern and PCI domain truncation/masking.
next prev parent reply other threads:[~2026-05-14 19:22 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-12 21:39 [PATCH v5 0/2] AMD Promontory 21 xHCI temperature sensor support Jihong Min
2026-05-12 21:39 ` [PATCH v5 1/2] usb: xhci-pci: add AMD Promontory 21 PCI glue Jihong Min
2026-05-14 0:40 ` sashiko-bot
2026-05-14 1:20 ` Guenter Roeck
2026-05-14 13:38 ` Jihong Min
2026-05-14 13:44 ` Jihong Min
2026-05-15 1:49 ` Guenter Roeck
2026-05-14 14:29 ` Jihong Min
2026-05-14 19:22 ` Guenter Roeck [this message]
2026-05-12 21:39 ` [PATCH v5 2/2] hwmon: add AMD Promontory 21 xHCI temperature sensor support Jihong Min
2026-05-14 1:00 ` sashiko-bot
2026-05-14 1:13 ` Guenter Roeck
2026-05-12 21:49 ` [PATCH v5 0/2] " Jihong Min
2026-05-13 14:48 ` Mario Limonciello
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