On Tue, 29 Apr 2025, 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, uapi/linux/pci_regs.h).
>
> The changes are purely non-functional cleanups, ensuring behavior remains
> identical to the original implementation.
>
> Signed-off-by: Hans Zhang <18255117159@xxxxxxx>
> ---
> Changes since v9:
> - None
>
> Changes since v8:
> - Split into patch 1/6, patch 2/6.
> - The
> drivers/pci/pci.c | 10 ++++++----
> include/uapi/linux/pci_regs.h | 2 ++
> 2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 4d7c9f64ea24..1c29e8f20cb5 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>
> @@ -30,6 +31,7 @@
> #include <asm/dma.h>
> #include <linux/aer.h>
> #include <linux/bitfield.h>
> +#include <uapi/linux/pci_regs.h>
linux/pci.h will pull this in through <uapi/linux/pci.h> so you don't need
to add it (basically anywhere).
> #include "pci.h"
>
> DEFINE_MUTEX(pci_slot_mutex);
> @@ -432,17 +434,17 @@ 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 ba326710f9c8..b59179e1210a 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -206,6 +206,8 @@
> /* 0x48-0x7f reserved */
>
> /* Capability lists */
> +#define PCI_CAP_ID_MASK 0x00ff
> +#define PCI_CAP_LIST_NEXT_MASK 0xff00
Consider adding a comment after the value as is done for most defines in
this file.
>
> #define PCI_CAP_LIST_ID 0 /* Capability ID */
> #define PCI_CAP_ID_PM 0x01 /* Power Management */
>
--
i.
