Re: [PATCH] PCI: Add PCI_RID_MASK macro

[Marc Zyngier <maz@kernel.org>]

On Mon, 16 Feb 2026 12:06:00 +0000,
Aksh Garg <a-garg7@ti.com> wrote:
> 
> Routing ID (RID) is a 16-bit value composed of bus number and devfn.

No. RID here means "Requester ID". Please lookup the PCI spec.

> Add a PCI_RID_MASK macro to eliminate the use of magic number 0xffff
> when masking for RIDs.

I'm not convinced this is universally true. Some RIDs (or RID-like
identifiers, such as Stream IDs and Device IDs) are larger than 16
bit, depending on the integration.

The fact that this particular integration uses a 16bit RID without any
extra qualifier in the upper bits doesn't make it universal.

> This provides a standard way for drivers to extract RIDs without
> resorting to magic numbers.
> 
> Signed-off-by: Aksh Garg <a-garg7@ti.com>
> ---
>  drivers/pci/controller/pcie-apple.c | 2 +-
>  include/linux/pci.h                 | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
> index 2d92fc79f6dd..6bf9fe102e2f 100644
> --- a/drivers/pci/controller/pcie-apple.c
> +++ b/drivers/pci/controller/pcie-apple.c
> @@ -802,7 +802,7 @@ static void apple_pcie_disable_device(struct pci_host_bridge *bridge, struct pci
>  		u32 val;
>  
>  		val = readl_relaxed(port_rid2sid_addr(port, idx));
> -		if ((val & 0xffff) == rid) {
> +		if ((val & PCI_RID_MASK) == rid) {
>  			apple_pcie_rid2sid_write(port, idx, 0);
>  			bitmap_release_region(port->sid_map, idx, 0);
>  			dev_dbg(&pdev->dev, "Released %x (%d)\n", val, idx);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 864775651c6f..e3d9730121c8 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -71,6 +71,7 @@
>  #define PCI_DEVID(bus, devfn)	((((u16)(bus)) << 8) | (devfn))
>  /* return bus from PCI devid = ((u16)bus_number) << 8) | devfn */
>  #define PCI_BUS_NUM(x) (((x) >> 8) & 0xff)
> +#define PCI_RID_MASK	0xffff

Even the naming of this macro clashes with the current nomenclature,
where we use PCI_DEVID()/pci_dev_id() to manipulate this information.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.