Subject: [PATCH] powerpc/pci: Enable PCI domains in /proc when PCI bus numbers are not unique

From: Pali Rohár <[email-masked]>
Date: Sat, 20 Aug 2022 13:51:13 +0200

On 32-bit powerpc systems with more PCIe controllers and more PCI domains,
where on more PCI domains are same PCI numbers, when kernel is compiled
with CONFIG_PROC_FS=y and CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT=y
options, kernel prints "proc_dir_entry 'pci/01' already registered" error
message.

  [    1.708861] ------------[ cut here ]------------
  [    1.713429] proc_dir_entry 'pci/01' already registered
  [    1.718595] WARNING: CPU: 0 PID: 1 at fs/proc/generic.c:377 proc_register+0x1a8/0x1ac
  [    1.726361] Modules linked in:
  [    1.729404] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W         5.19.0-rc5-0caacb197b677410bdac81bc34f05235+ #109
  [    1.740183] NIP:  c02846e8 LR: c02846e8 CTR: c0015154
  [    1.745225] REGS: c146fc90 TRAP: 0700   Tainted: G        W          (5.19.0-rc5-0caacb197b677410bdac81bc34f05235+)
  [    1.755657] MSR:  00029000 <CE,EE,ME>  CR: 28000822  XER: 00000000
  [    1.761829]
  [    1.761829] GPR00: c02846e8 c146fd80 c14a8000 0000002a 3fffefff c146fc40 c146fc38 00000000
  [    1.761829] GPR08: 3fffefff 00000000 00000000 c10ac04c 24000824 00000000 c0004548 00000000
  [    1.761829] GPR16: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000007
  [    1.761829] GPR24: c10000d0 c167da54 c167da00 c1120000 c167dd6c c10b4abc c167dc58 c167dd00
  [    1.796707] NIP [c02846e8] proc_register+0x1a8/0x1ac
  [    1.801663] LR [c02846e8] proc_register+0x1a8/0x1ac
  [    1.806532] Call Trace:
  [    1.808966] [c146fd80] [c02846e8] proc_register+0x1a8/0x1ac (unreliable)
  [    1.815659] [c146fdb0] [c028481c] _proc_mkdir+0x78/0xa4
  [    1.820875] [c146fdd0] [c05a92e4] pci_proc_attach_device+0x11c/0x168
  [    1.827221] [c146fe10] [c101f7a4] pci_proc_init+0x80/0x98
  [    1.832611] [c146fe30] [c0004150] do_one_initcall+0x80/0x284
  [    1.838262] [c146fea0] [c10011a8] kernel_init_freeable+0x1f4/0x2a0
  [    1.844434] [c146fee0] [c000456c] kernel_init+0x24/0x150
  [    1.849737] [c146ff00] [c001326c] ret_from_kernel_thread+0x5c/0x64
  [    1.855910] Instruction dump:
  [    1.858866] 83810020 83a10024 83c10028 83e1002c 38210030 4e800020 809a0064 3c60c0a8
  [    1.866602] 7f85e378 3863af28 4cc63182 4bdb8155 <0fe00000> 9421ffe0 39200000 7c0802a6
  [    1.874513] ---[ end trace 0000000000000000 ]---

This regression started appearing after commit 566356813082 ("powerpc/pci:
Add config option for using all 256 PCI buses") in case in each mPCIe slot
is connected PCIe card and therefore PCI bus 1 is populated in for every
PCIe controller / PCI domain.

The reason is that PCI procfs code expects that when PCI bus numbers are
not unique across all PCI domains, function pci_proc_domain() returns true
for domain dependent buses.

Fix this issue by setting PCI_ENABLE_PROC_DOMAINS and PCI_COMPAT_DOMAIN_0
flags for 32-bit powerpc code when CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT
is enabled. Same approach is already implemented for 64-bit powerpc code
(where PCI bus numbers are always domain dependent).

Fixes: 566356813082 ("powerpc/pci: Add config option for using all 256 PCI buses")
Signed-off-by: Pali Rohár <[email-masked]>
---
 arch/powerpc/kernel/pci_32.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/powerpc/kernel/pci_32.c b/arch/powerpc/kernel/pci_32.c
index ffc4e1928c80..8acbc9592ebb 100644
--- a/arch/powerpc/kernel/pci_32.c
+++ b/arch/powerpc/kernel/pci_32.c
@@ -249,6 +249,15 @@ static int __init pcibios_init(void)
 
 	printk(KERN_INFO "PCI: Probing PCI hardware\n");
 
+#ifdef CONFIG_PPC_PCI_BUS_NUM_DOMAIN_DEPENDENT
+	/*
+	 * Enable PCI domains in /proc when PCI bus numbers are not unique
+	 * across all PCI domains to prevent conflicts. And keep PCI domain 0
+	 * backward compatible in /proc for video cards.
+	 */
+	pci_add_flags(PCI_ENABLE_PROC_DOMAINS | PCI_COMPAT_DOMAIN_0);
+#endif
+
 	if (pci_has_flag(PCI_REASSIGN_ALL_BUS))
 		pci_assign_all_buses = 1;
 
-- 
2.20.1