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PCI: Clean up __pci_find_next_cap_ttl() readability

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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@163.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Acked-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20250813144529.303548-2-18255117159@163.com
This commit is contained in:
Hans Zhang 2025-08-13 22:45:24 +08:00 committed by Bjorn Helgaas
parent 8f5ae30d69
commit 37d1ade896
2 changed files with 8 additions and 4 deletions
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9
drivers/pci/pci.c
View File

@ -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;
}

3
include/uapi/linux/pci_regs.h
View File

@ -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 */