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Message-Id: <20250321040358.360755-2-18255117159@163.com>
Date: Fri, 21 Mar 2025 12:03:55 +0800
From: Hans Zhang <18255117159@....com>
To: lpieralisi@...nel.org
Cc: kw@...ux.com,
manivannan.sadhasivam@...aro.org,
robh@...nel.org,
bhelgaas@...gle.com,
jingoohan1@...il.com,
thomas.richard@...tlin.com,
linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org,
Hans Zhang <18255117159@....com>
Subject: [v3 1/4] PCI: Introduce generic capability search functions
Existing controller drivers (e.g., DWC, custom out-of-tree drivers)
duplicate logic for scanning PCI capability lists. This creates
maintenance burdens and risks inconsistencies.
To resolve this:
1. Add pci_generic_find_capability() and pci_generic_find_ext_capability()
in drivers/pci/pci.c, accepting controller-specific read functions
and device data as parameters.
2. Refactor dwc_pcie_find_capability() and similar functions to utilize
these new generic interfaces.
3. Update out-of-tree drivers to leverage the common implementation,
eliminating code duplication.
This approach:
- Centralizes critical PCI capability scanning logic
- Allows flexible adaptation to varied hardware access methods
- Reduces future maintenance overhead
- Aligns with kernel code reuse best practices
Tested with DWC PCIe controller and CDNS PCIe drivers.
Signed-off-by: Hans Zhang <18255117159@....com>
---
drivers/pci/pci.c | 83 +++++++++++++++++++++++++++++++++++++++++++++
include/linux/pci.h | 13 ++++++-
2 files changed, 95 insertions(+), 1 deletion(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 869d204a70a3..d686d89d211e 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -612,6 +612,89 @@ u16 pci_find_ext_capability(struct pci_dev *dev, int cap)
}
EXPORT_SYMBOL_GPL(pci_find_ext_capability);
+/*
+ * These interfaces resemble the pci_find_*capability() interfaces, but these
+ * are for configuring host controllers, which are bridges *to* PCI devices but
+ * are not PCI devices themselves.
+ */
+static u8 __pci_generic_find_next_cap(void *priv, pci_generic_read_cfg read_cfg,
+ u8 cap_ptr, u8 cap)
+{
+ u8 cap_id, next_cap_ptr;
+ u16 reg;
+
+ if (!cap_ptr)
+ return 0;
+
+ reg = read_cfg(priv, cap_ptr, 2);
+ cap_id = (reg & 0x00ff);
+
+ if (cap_id > PCI_CAP_ID_MAX)
+ return 0;
+
+ if (cap_id == cap)
+ return cap_ptr;
+
+ next_cap_ptr = (reg & 0xff00) >> 8;
+ return __pci_generic_find_next_cap(priv, read_cfg, next_cap_ptr, cap);
+}
+
+u8 pci_generic_find_capability(void *priv, pci_generic_read_cfg read_cfg,
+ u8 cap)
+{
+ u8 next_cap_ptr;
+ u16 reg;
+
+ reg = read_cfg(priv, PCI_CAPABILITY_LIST, 2);
+ next_cap_ptr = (reg & 0x00ff);
+
+ return __pci_generic_find_next_cap(priv, read_cfg, next_cap_ptr, cap);
+}
+EXPORT_SYMBOL_GPL(pci_generic_find_capability);
+
+static u16 pci_generic_find_next_ext_capability(void *priv,
+ pci_generic_read_cfg read_cfg,
+ u16 start, u8 cap)
+{
+ u32 header;
+ int ttl;
+ int pos = PCI_CFG_SPACE_SIZE;
+
+ /* minimum 8 bytes per capability */
+ ttl = (PCI_CFG_SPACE_EXP_SIZE - PCI_CFG_SPACE_SIZE) / 8;
+
+ if (start)
+ pos = start;
+
+ header = read_cfg(priv, pos, 4);
+ /*
+ * If we have no capabilities, this is indicated by cap ID,
+ * cap version and next pointer all being 0.
+ */
+ if (header == 0)
+ return 0;
+
+ while (ttl-- > 0) {
+ if (PCI_EXT_CAP_ID(header) == cap && pos != start)
+ return pos;
+
+ pos = PCI_EXT_CAP_NEXT(header);
+ if (pos < PCI_CFG_SPACE_SIZE)
+ break;
+
+ header = read_cfg(priv, pos, 4);
+ }
+
+ return 0;
+}
+
+u16 pci_generic_find_ext_capability(void *priv, pci_generic_read_cfg read_cfg,
+ int cap)
+{
+ return pci_generic_find_next_ext_capability(priv, read_cfg, 0, cap);
+}
+EXPORT_SYMBOL_GPL(pci_generic_find_ext_capability);
+
/**
* pci_get_dsn - Read and return the 8-byte Device Serial Number
* @dev: PCI device to query
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 47b31ad724fa..48c2b45a4d04 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1205,6 +1205,11 @@ u8 pci_find_ht_capability(struct pci_dev *dev, int ht_cap);
u8 pci_find_next_ht_capability(struct pci_dev *dev, u8 pos, int ht_cap);
u16 pci_find_ext_capability(struct pci_dev *dev, int cap);
u16 pci_find_next_ext_capability(struct pci_dev *dev, u16 pos, int cap);
+typedef u32 (*pci_generic_read_cfg)(void *priv, int where, int size);
+u8 pci_generic_find_capability(void *priv, pci_generic_read_cfg read_cfg,
+ u8 cap);
+u16 pci_generic_find_ext_capability(void *priv, pci_generic_read_cfg read_cfg,
+ u8 cap);
struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
u16 pci_find_vsec_capability(struct pci_dev *dev, u16 vendor, int cap);
u16 pci_find_dvsec_capability(struct pci_dev *dev, u16 vendor, u16 dvsec);
@@ -2012,7 +2017,13 @@ static inline u8 pci_find_next_capability(struct pci_dev *dev, u8 post, int cap)
{ return 0; }
static inline u16 pci_find_ext_capability(struct pci_dev *dev, int cap)
{ return 0; }
-
+typedef u32 (*pci_generic_read_cfg)(void *priv, int where, int size);
+u8 pci_generic_find_capability(void *priv, pci_generic_read_cfg read_cfg,
+ u8 cap)
+{ return 0; }
+u16 pci_generic_find_ext_capability(void *priv, pci_generic_read_cfg read_cfg,
+ u8 cap)
+{ return 0; }
static inline u64 pci_get_dsn(struct pci_dev *dev)
{ return 0; }
--
2.25.1
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