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Message-Id: <20250323164852.430546-2-18255117159@163.com>
Date: Mon, 24 Mar 2025 00:48:48 +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: [v6 1/5] 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:
Add pci_host_bridge_find_*capability() in pci-host-helpers.c, accepting
controller-specific read functions and device data as parameters.
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
Signed-off-by: Hans Zhang <18255117159@....com>
---
Changes since v5:
https://lore.kernel.org/linux-pci/20250321163803.391056-2-18255117159@163.com
- If you put the helpers in drivers/pci/pci.c, they unnecessarily enlarge
the kernel's .text section even if it's known already at compile time
that they're never going to be used (e.g. on x86).
- Move the API for find capabilitys to a new file called
pci-host-helpers.c.
Changes since v4:
https://lore.kernel.org/linux-pci/20250321101710.371480-2-18255117159@163.com
- Resolved [v4 1/4] compilation warning.
- The patch commit message were modified.
---
drivers/pci/controller/Kconfig | 17 ++++
drivers/pci/controller/Makefile | 1 +
drivers/pci/controller/pci-host-helpers.c | 98 +++++++++++++++++++++++
drivers/pci/pci.h | 7 ++
4 files changed, 123 insertions(+)
create mode 100644 drivers/pci/controller/pci-host-helpers.c
diff --git a/drivers/pci/controller/Kconfig b/drivers/pci/controller/Kconfig
index 9800b7681054..0020a892a55b 100644
--- a/drivers/pci/controller/Kconfig
+++ b/drivers/pci/controller/Kconfig
@@ -132,6 +132,23 @@ config PCI_HOST_GENERIC
Say Y here if you want to support a simple generic PCI host
controller, such as the one emulated by kvmtool.
+config PCI_HOST_HELPERS
+ bool
+ prompt "PCI Host Controller Helper Functions" if EXPERT
+ help
+ This provides common infrastructure for PCI host controller drivers to
+ handle PCI capability scanning and other shared operations. The helper
+ functions eliminate code duplication across controller drivers.
+
+ These functions are used by PCI controller drivers that need to scan
+ PCI capabilities using controller-specific access methods (e.g. when
+ the controller is behind a non-standard configuration space).
+
+ If you are using any PCI host controller drivers that require these
+ helpers (such as DesignWare, Cadence, etc), this will be
+ automatically selected. Say N unless you are developing a custom PCI
+ host controller driver.
+
config PCIE_HISI_ERR
depends on ACPI_APEI_GHES && (ARM64 || COMPILE_TEST)
bool "HiSilicon HIP PCIe controller error handling driver"
diff --git a/drivers/pci/controller/Makefile b/drivers/pci/controller/Makefile
index 038ccbd9e3ba..e80091eb7597 100644
--- a/drivers/pci/controller/Makefile
+++ b/drivers/pci/controller/Makefile
@@ -12,6 +12,7 @@ obj-$(CONFIG_PCIE_RCAR_HOST) += pcie-rcar.o pcie-rcar-host.o
obj-$(CONFIG_PCIE_RCAR_EP) += pcie-rcar.o pcie-rcar-ep.o
obj-$(CONFIG_PCI_HOST_COMMON) += pci-host-common.o
obj-$(CONFIG_PCI_HOST_GENERIC) += pci-host-generic.o
+obj-$(CONFIG_PCI_HOST_HELPERS) += pci-host-helpers.o
obj-$(CONFIG_PCI_HOST_THUNDER_ECAM) += pci-thunder-ecam.o
obj-$(CONFIG_PCI_HOST_THUNDER_PEM) += pci-thunder-pem.o
obj-$(CONFIG_PCIE_XILINX) += pcie-xilinx.o
diff --git a/drivers/pci/controller/pci-host-helpers.c b/drivers/pci/controller/pci-host-helpers.c
new file mode 100644
index 000000000000..cd261a281c60
--- /dev/null
+++ b/drivers/pci/controller/pci-host-helpers.c
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * PCI Host Controller Helper Functions
+ *
+ * Copyright (C) 2025 Hans Zhang
+ *
+ * Author: Hans Zhang <18255117159@....com>
+ */
+
+#include <linux/pci.h>
+
+#include "../pci.h"
+
+/*
+ * 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_host_bridge_find_next_cap(void *priv,
+ pci_host_bridge_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_host_bridge_find_next_cap(priv, read_cfg, next_cap_ptr,
+ cap);
+}
+
+u8 pci_host_bridge_find_capability(void *priv,
+ pci_host_bridge_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_host_bridge_find_next_cap(priv, read_cfg, next_cap_ptr,
+ cap);
+}
+EXPORT_SYMBOL_GPL(pci_host_bridge_find_capability);
+
+static u16 pci_host_bridge_find_next_ext_capability(
+ void *priv, pci_host_bridge_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_host_bridge_find_ext_capability(void *priv,
+ pci_host_bridge_read_cfg read_cfg,
+ u8 cap)
+{
+ return pci_host_bridge_find_next_ext_capability(priv, read_cfg, 0, cap);
+}
+EXPORT_SYMBOL_GPL(pci_host_bridge_find_ext_capability);
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 01e51db8d285..8d1c919cbfef 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -1034,4 +1034,11 @@ void pcim_release_region(struct pci_dev *pdev, int bar);
(PCI_CONF1_ADDRESS(bus, dev, func, reg) | \
PCI_CONF1_EXT_REG(reg))
+typedef u32 (*pci_host_bridge_read_cfg)(void *priv, int where, int size);
+u8 pci_host_bridge_find_capability(void *priv,
+ pci_host_bridge_read_cfg read_cfg, u8 cap);
+u16 pci_host_bridge_find_ext_capability(void *priv,
+ pci_host_bridge_read_cfg read_cfg,
+ u8 cap);
+
#endif /* DRIVERS_PCI_H */
--
2.25.1
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