On Wed, 2025-08-13 at 22:45 +0800, Hans Zhang wrote:
> Refactor the __pci_find_next_cap_ttl() to improve code clarity:
> - Replace magic number 0x40 with PCI_STD_HEADER_SIZEOF.
> - Use ALIGN_DOWN() for position alignment instead of manual bitmask.
> - Extract PCI capability fields via FIELD_GET() with standardized masks.
> - Add necessary headers (linux/align.h).
>
> No functional changes intended.
>
> Signed-off-by: Hans Zhang <18255117159@xxxxxxx>
> Acked-by: Manivannan Sadhasivam <mani@xxxxxxxxxx>
> ---
> drivers/pci/pci.c | 9 +++++----
> include/uapi/linux/pci_regs.h | 3 +++
> 2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b0f4d98036cd..40a5c87d9a6b 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -9,6 +9,7 @@
> */
>
> #include <linux/acpi.h>
> +#include <linux/align.h>
> #include <linux/kernel.h>
> #include <linux/delay.h>
> #include <linux/dmi.h>
> @@ -432,17 +433,17 @@ static u8 __pci_find_next_cap_ttl(struct pci_bus *bus, unsigned int devfn,
> pci_bus_read_config_byte(bus, devfn, pos, &pos);
>
> while ((*ttl)--) {
> - if (pos < 0x40)
> + if (pos < PCI_STD_HEADER_SIZEOF)
> break;
> - pos &= ~3;
> + pos = ALIGN_DOWN(pos, 4);
> pci_bus_read_config_word(bus, devfn, pos, &ent);
>
> - id = ent & 0xff;
> + id = FIELD_GET(PCI_CAP_ID_MASK, ent);
> if (id == 0xff)
> break;
> if (id == cap)
> return pos;
> - pos = (ent >> 8);
> + pos = FIELD_GET(PCI_CAP_LIST_NEXT_MASK, ent);
> }
> return 0;
> }
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index f5b17745de60..1bba99b46227 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -207,6 +207,9 @@
>
> /* Capability lists */
>
> +#define PCI_CAP_ID_MASK 0x00ff /* Capability ID mask */
> +#define PCI_CAP_LIST_NEXT_MASK 0xff00 /* Next Capability Pointer mask */
> +
> #define PCI_CAP_LIST_ID 0 /* Capability ID */
> #define PCI_CAP_ID_PM 0x01 /* Power Management */
> #define PCI_CAP_ID_AGP 0x02 /* Accelerated Graphics Port */
Hi Hans,
I like your approach to replace the magic numbers here. If you went
further to replace the single pci_bus_read_config_word() with two
single-byte reads at the appropriate places - for CAP_ID and
CAP_LIST_NEXT - you could even go with the already existing offset
defines PCI_CAP_LIST_ID and PCI_CAP_LIST_NEXT from pci_regs.h.
But that might be a more intricate change and involves more HW accesses
than what it's worth.
So feel free to add my
Reviewed-by: Gerd Bayer <gbayer@xxxxxxxxxxxxx>
Thanks,
Gerd
