[PATCH] riscv: align pcie bus assign logic with ARM64

[sun.wenhan]

From: sun wenhan <sun.wenhan@xxxxxxxxxx>


RISC-V currently relies on the asm-generic default of
pcibios_assign_all_busses() returning 1, so the kernel always
re-assigns all PCI bus numbers and ignores the bus numbers already
set up by the firmware. This has two downsides:

1. As UEFI 2.8 has brought mature firmware support to RISC-V servers,
the OS can trust and inherit the PCI bus enumeration done by the
BIOS, skipping a redundant re-enumeration at boot and improving
the boot time.

2. The unconditional re-assignment causes bus numbering conflicts
during PCI rescan. When a root port that is not the last one in
the hierarchy is removed and the bus is rescanned, the kernel
fails with:

pci_bus 0000:01: busn_res: can not insert [bus 01-ff] under
[bus 00-ff] (conflicts with (null) [bus 02])

as reported for the same generic code in commit bd8cbe66c01d
("PCI: Make PCI bus renumbering configurable to avoid rescan
conflicts").

Define pcibios_assign_all_busses() the same way as ARM64,
so that RISC-V also preserves the bus numbers assigned by the
firmware by default instead of always re-assigning them. This keeps
RISC-V consistent with the other major architectures.

Signed-off-by: sun wenhan <sun.wenhan@xxxxxxxxxx>
---
arch/riscv/include/asm/pci.h | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/arch/riscv/include/asm/pci.h b/arch/riscv/include/asm/pci.h
index cc2a184cfc2e..b2f91abebd61 100644
--- a/arch/riscv/include/asm/pci.h
+++ b/arch/riscv/include/asm/pci.h
@@ -15,6 +15,11 @@
#define PCIBIOS_MIN_IO   4
#define PCIBIOS_MIN_MEM    16

+/*
+ * Set to 1 if the kernel should re-assign all PCI bus numbers
+ */
+#define pcibios_assign_all_busses() (pci_has_flag(PCI_REASSIGN_ALL_BUS))
+
#if defined(CONFIG_PCI) && defined(CONFIG_NUMA)
static inline int pcibus_to_node(struct pci_bus *bus)
{
--
2.27.0