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Message-Id: <20250716161203.83823-4-18255117159@163.com>
Date: Thu, 17 Jul 2025 00:11:59 +0800
From: Hans Zhang <18255117159@....com>
To: lpieralisi@...nel.org,
kwilczynski@...nel.org,
bhelgaas@...gle.com,
helgaas@...nel.org,
jingoohan1@...il.com,
mani@...nel.org
Cc: robh@...nel.org,
ilpo.jarvinen@...ux.intel.com,
linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org,
Hans Zhang <18255117159@....com>
Subject: [PATCH v14 3/7] PCI: Refactor standard capability search into common macro
The PCI Capability search functionality is duplicated across the PCI core
and several controller drivers. The core's current implementation requires
fully initialized PCI device and bus structures, which prevents controller
drivers from using it during early initialization phases before these
structures are available.
Move the Capability search logic into a header-based macro that accepts a
config space accessor function as an argument. This enables controller
drivers to perform Capability discovery using their early access
mechanisms prior to full device initialization while sharing the
Capability search code.
Convert the existing PCI core Capability search implementation to use this
new macro. Controller drivers can later use the same macros with their
early access mechanisms while maintaining the existing protection against
infinite loops through preserved TTL checks.
The ttl parameter was originally an additional safeguard to prevent
infinite loops in corrupted config space. However, the
PCI_FIND_NEXT_CAP() macro already enforces a TTL limit internally.
Removing redundant ttl handling simplifies the interface while maintaining
the safety guarantee. This aligns with the macro's design intent of
encapsulating TTL management.
Signed-off-by: Hans Zhang <18255117159@....com>
---
Changes since v13:
- Split patch for searching standard capability.
Changes since v12:
- Delete __pci_find_next_cap, use PCI_FIND_NEXT_CAP_TTL() directly.
- Modify the doc description of the function.
Changes since v11:
- Add #include <linux/bitfield.h>, solve the compilation warnings caused by the subsequent patch calls.
Changes since v10:
- Remove #include <uapi/linux/pci_regs.h>.
- The patch commit message were modified.
Changes since v9:
- None
Changes since v8:
- The patch commit message were modified.
---
drivers/pci/pci.c | 42 ++++++++----------------------------------
drivers/pci/pci.h | 45 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 53 insertions(+), 34 deletions(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 1d1d147d007a..c590f697c011 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -9,7 +9,6 @@
*/
#include <linux/acpi.h>
-#include <linux/align.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/dmi.h>
@@ -424,36 +423,10 @@ static int pci_dev_str_match(struct pci_dev *dev, const char *p,
return 1;
}
-static u8 __pci_find_next_cap_ttl(struct pci_bus *bus, unsigned int devfn,
- u8 pos, int cap, int *ttl)
-{
- u8 id;
- u16 ent;
-
- pci_bus_read_config_byte(bus, devfn, pos, &pos);
-
- while ((*ttl)--) {
- if (pos < PCI_STD_HEADER_SIZEOF)
- break;
- pos = ALIGN_DOWN(pos, 4);
- pci_bus_read_config_word(bus, devfn, pos, &ent);
-
- id = FIELD_GET(PCI_CAP_ID_MASK, ent);
- if (id == 0xff)
- break;
- if (id == cap)
- return pos;
- pos = FIELD_GET(PCI_CAP_LIST_NEXT_MASK, ent);
- }
- return 0;
-}
-
static u8 __pci_find_next_cap(struct pci_bus *bus, unsigned int devfn,
u8 pos, int cap)
{
- int ttl = PCI_FIND_CAP_TTL;
-
- return __pci_find_next_cap_ttl(bus, devfn, pos, cap, &ttl);
+ return PCI_FIND_NEXT_CAP(pci_bus_read_config, pos, cap, bus, devfn);
}
u8 pci_find_next_capability(struct pci_dev *dev, u8 pos, int cap)
@@ -649,7 +622,7 @@ EXPORT_SYMBOL_GPL(pci_get_dsn);
static u8 __pci_find_next_ht_cap(struct pci_dev *dev, u8 pos, int ht_cap)
{
- int rc, ttl = PCI_FIND_CAP_TTL;
+ int rc;
u8 cap, mask;
if (ht_cap == HT_CAPTYPE_SLAVE || ht_cap == HT_CAPTYPE_HOST)
@@ -657,8 +630,8 @@ static u8 __pci_find_next_ht_cap(struct pci_dev *dev, u8 pos, int ht_cap)
else
mask = HT_5BIT_CAP_MASK;
- pos = __pci_find_next_cap_ttl(dev->bus, dev->devfn, pos,
- PCI_CAP_ID_HT, &ttl);
+ pos = PCI_FIND_NEXT_CAP(pci_bus_read_config, pos,
+ PCI_CAP_ID_HT, dev->bus, dev->devfn);
while (pos) {
rc = pci_read_config_byte(dev, pos + 3, &cap);
if (rc != PCIBIOS_SUCCESSFUL)
@@ -667,9 +640,10 @@ static u8 __pci_find_next_ht_cap(struct pci_dev *dev, u8 pos, int ht_cap)
if ((cap & mask) == ht_cap)
return pos;
- pos = __pci_find_next_cap_ttl(dev->bus, dev->devfn,
- pos + PCI_CAP_LIST_NEXT,
- PCI_CAP_ID_HT, &ttl);
+ pos = PCI_FIND_NEXT_CAP(pci_bus_read_config,
+ pos + PCI_CAP_LIST_NEXT,
+ PCI_CAP_ID_HT, dev->bus,
+ dev->devfn);
}
return 0;
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index e7d31ed56731..7465501a21e3 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -2,6 +2,8 @@
#ifndef DRIVERS_PCI_H
#define DRIVERS_PCI_H
+#include <linux/align.h>
+#include <linux/bitfield.h>
#include <linux/pci.h>
struct pcie_tlp_log;
@@ -93,6 +95,49 @@ bool pcie_cap_has_rtctl(const struct pci_dev *dev);
int pci_bus_read_config(void *priv, unsigned int devfn, int where, u32 size,
u32 *val);
+/* Standard Capability finder */
+/**
+ * PCI_FIND_NEXT_CAP - Find a PCI standard capability
+ * @read_cfg: Function pointer for reading PCI config space
+ * @start: Starting position to begin search
+ * @cap: Capability ID to find
+ * @args: Arguments to pass to read_cfg function
+ *
+ * Iterates through the capability list in PCI config space to find
+ * @cap. Implements TTL (time-to-live) protection against infinite loops.
+ *
+ * Returns: Position of the capability if found, 0 otherwise.
+ */
+#define PCI_FIND_NEXT_CAP(read_cfg, start, cap, args...) \
+({ \
+ int __ttl = PCI_FIND_CAP_TTL; \
+ u8 __id, __found_pos = 0; \
+ u8 __pos = (start); \
+ u16 __ent; \
+ \
+ read_cfg(args, __pos, 1, (u32 *)&__pos); \
+ \
+ while (__ttl--) { \
+ if (__pos < PCI_STD_HEADER_SIZEOF) \
+ break; \
+ \
+ __pos = ALIGN_DOWN(__pos, 4); \
+ read_cfg(args, __pos, 2, (u32 *)&__ent); \
+ \
+ __id = FIELD_GET(PCI_CAP_ID_MASK, __ent); \
+ if (__id == 0xff) \
+ break; \
+ \
+ if (__id == (cap)) { \
+ __found_pos = __pos; \
+ break; \
+ } \
+ \
+ __pos = FIELD_GET(PCI_CAP_LIST_NEXT_MASK, __ent); \
+ } \
+ __found_pos; \
+})
+
/* Functions internal to the PCI core code */
#ifdef CONFIG_DMI
--
2.25.1
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