[PATCH RFC v2 0/3] PCI: rockchip-host: Handle unavailable downstream config space

[PATCH RFC v2 0/3] PCI: rockchip-host: Handle unavailable downstream config space

[Matt Thompson via B4 Relay]

On a RockPro64 v2.1 with a Kintex-7 FPGA endpoint, a downstream
vendor-ID read during a PCI rescan raised a synchronous external
abort (ESR 0x96000210) in rockchip_pcie_rd_conf(). The rescan task
exited with IRQs disabled and a watchdog lockup followed.

The first patch skips downstream config accesses while the controller
reports the link unavailable. The remaining patches handle synchronous
external aborts on explicitly annotated arm64 config reads, including
when the link changes after the status check. The final patch also
clears the AXI link-down latch before downstream config accesses
once the controller reports the link ready.

The arm64 change is limited to marked load instructions. Asynchronous
SError, BAR accesses, and config writes that race a link change are
outside that recovery path. Feedback on the exception-table interface
and whether the controller can handle absent completions directly is
welcome.

A related discussion covers an RK3399 endpoint that trains but fails
to answer config requests:
https://lore.kernel.org/linux-pci/20261024-rockchip-pcie-resume-v1-0-58e54a5cf5f1@iav.lv/

Validation: applied these three RFC patches to upstream commit
97d73c8251226cf27cc6656b4c542869bb8c69fa and booted the resulting
7.4.0-rc2 kernel on a RockPro64 v2.1. The test config enabled Rust
and built in the required board drivers.

Three test cycles completed on the v2 kernel. Each removed the FPGA
from Linux, disabled the link and rescanned, then re-enabled the link,
requested retraining and rescanned. The FPGA stayed absent in each
disabled scan and returned at 01:00.0 after each retrain without a host
driver rebind. The log showed no synchronous external abort or
watchdog lockup. The test did not establish whether the arm64 fixup ran.

---
Changes in v2:
- Restrict the MMIO read fixup to the SEA path and exclude its
  exception-table type from user-access classification.
- Look up the guarded instruction once on the SEA path.
- Use the standard arm64 register-number encoding helpers in
  the exception-table macro (Sashiko review).
- Link to v1: https://patch.msgid.link/20261113-rfc-b4-v1-0-b91dcb502250@boondocker.io

---
Matt Thompson (3):
      PCI: rockchip-host: Skip downstream config access while link is down
      arm64: Allow synchronous abort fixups for guarded MMIO reads
      PCI: rockchip-host: Recover downstream configuration access

 arch/arm64/include/asm/asm-extable.h        | 15 +++++++
 arch/arm64/mm/extable.c                     | 20 +++++++++
 arch/arm64/mm/fault.c                       |  4 ++
 drivers/pci/controller/pcie-rockchip-host.c | 68 +++++++++++++++++++++++++++++
 drivers/pci/controller/pcie-rockchip.h      |  1 +
 5 files changed, 108 insertions(+)
---
base-commit: a72c40386d63746568fb027900faaa8ec0054127
change-id: 20261113-rfc-b4-6b795b536d9a

Best regards,
--  
Matt Thompson <matt@boondocker.io>

[PATCH RFC v2 1/3] PCI: rockchip-host: Skip downstream config access while link is down

[Matt Thompson via B4 Relay]

From: Matt Thompson <matt@boondocker.io>

On a RockPro64, a PCI bus rescan with the downstream FPGA unavailable
faulted in rockchip_pcie_rd_conf() during a vendor ID read. The rescan
task exited with interrupts disabled and the watchdog reported a lockup.

Check the controller's link-up and link-training status before issuing
downstream config requests. Return PCIBIOS_DEVICE_NOT_FOUND while the
link is unavailable. Root port config access still uses the local
controller registers.

This check cannot prevent the link from dropping during the transaction.

Signed-off-by: Matt Thompson <matt@boondocker.io>
---
 drivers/pci/controller/pcie-rockchip-host.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/pci/controller/pcie-rockchip-host.c b/drivers/pci/controller/pcie-rockchip-host.c
index 5b071bd..35105c1 100644
--- a/drivers/pci/controller/pcie-rockchip-host.c
+++ b/drivers/pci/controller/pcie-rockchip-host.c
@@ -143,12 +143,23 @@ static int rockchip_pcie_wr_own_conf(struct rockchip_pcie *rockchip,
 	return PCIBIOS_SUCCESSFUL;
 }
 
+static bool rockchip_pcie_downstream_ready(struct rockchip_pcie *rockchip)
+{
+	return PCIE_LINK_UP(rockchip_pcie_read(rockchip, PCIE_CLIENT_BASIC_STATUS1)) &&
+	       PCIE_LINK_TRAINING_DONE(rockchip_pcie_read(rockchip, PCIE_CORE_CTRL));
+}
+
 static int rockchip_pcie_rd_other_conf(struct rockchip_pcie *rockchip,
 				       struct pci_bus *bus, u32 devfn,
 				       int where, int size, u32 *val)
 {
 	void __iomem *addr;
 
+	if (!rockchip_pcie_downstream_ready(rockchip)) {
+		*val = ~0U;
+		return PCIBIOS_DEVICE_NOT_FOUND;
+	}
+
 	addr = rockchip->reg_base + PCIE_ECAM_OFFSET(bus->number, devfn, where);
 
 	if (!IS_ALIGNED((uintptr_t)addr, size)) {
@@ -182,6 +193,9 @@ static int rockchip_pcie_wr_other_conf(struct rockchip_pcie *rockchip,
 {
 	void __iomem *addr;
 
+	if (!rockchip_pcie_downstream_ready(rockchip))
+		return PCIBIOS_DEVICE_NOT_FOUND;
+
 	addr = rockchip->reg_base + PCIE_ECAM_OFFSET(bus->number, devfn, where);
 
 	if (!IS_ALIGNED((uintptr_t)addr, size))

-- 
Git-155)

[PATCH RFC v2 2/3] arm64: Allow synchronous abort fixups for guarded MMIO reads

[Matt Thompson via B4 Relay]

From: Matt Thompson <matt@boondocker.io>

An RK3399 PCI configuration read can raise a synchronous external data
abort if it does not get a usable response. Allow an explicitly annotated
MMIO load to return an error in this case.

Match only a current-EL synchronous external abort on a read instruction
with the new exception table type. Keep existing handling for other
faults, including asynchronous SError and translation table walk aborts.

Signed-off-by: Matt Thompson <matt@boondocker.io>
---
 arch/arm64/include/asm/asm-extable.h | 15 +++++++++++++++
 arch/arm64/mm/extable.c              | 20 ++++++++++++++++++++
 arch/arm64/mm/fault.c                |  4 ++++
 3 files changed, 39 insertions(+)

diff --git a/arch/arm64/include/asm/asm-extable.h b/arch/arm64/include/asm/asm-extable.h
index d67e2fd..ac78167 100644
--- a/arch/arm64/include/asm/asm-extable.h
+++ b/arch/arm64/include/asm/asm-extable.h
@@ -11,6 +11,7 @@
 #define EX_TYPE_KACCESS_ERR_ZERO	3
 #define EX_TYPE_UACCESS_CPY		4
 #define EX_TYPE_LOAD_UNALIGNED_ZEROPAD	5
+#define EX_TYPE_MMIO_READ_ERR_ZERO	6
 
 /* Data fields for EX_TYPE_UACCESS_ERR_ZERO */
 #define EX_DATA_REG_ERR_SHIFT	0
@@ -80,6 +81,11 @@
 #else /* __ASSEMBLER__ */
 
 #include <linux/stringify.h>
+#include <linux/types.h>
+
+struct pt_regs;
+
+bool fixup_sea_exception(struct pt_regs *regs, unsigned long esr);
 
 #define __ASM_EXTABLE_RAW(insn, fixup, type, data)	\
 	".pushsection	__ex_table, \"a\"\n"		\
@@ -111,6 +117,15 @@
 			    EX_DATA_REG(ZERO, zero)			\
 			  ")")
 
+#define _ASM_EXTABLE_MMIO_READ_ERR_ZERO(insn, fixup, err, zero)		\
+	__DEFINE_ASM_GPR_NUMS						\
+	__ASM_EXTABLE_RAW(#insn, #fixup,				\
+			  __stringify(EX_TYPE_MMIO_READ_ERR_ZERO),	\
+			  "("						\
+			    EX_DATA_REG(ERR, err) " | "			\
+			    EX_DATA_REG(ZERO, zero)			\
+			  ")")
+
 #define _ASM_EXTABLE_UACCESS_ERR(insn, fixup, err)			\
 	_ASM_EXTABLE_UACCESS_ERR_ZERO(insn, fixup, err, wzr)
 
diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
index 299a244..dcb84d8 100644
--- a/arch/arm64/mm/extable.c
+++ b/arch/arm64/mm/extable.c
@@ -28,6 +28,8 @@ bool insn_may_access_user(unsigned long addr, unsigned long esr)
 		return false;
 
 	switch (ex->type) {
+	case EX_TYPE_MMIO_READ_ERR_ZERO:
+		return false;
 	case EX_TYPE_UACCESS_CPY:
 		return cpy_faulted_on_uaccess(ex, esr);
 	default:
@@ -101,6 +103,8 @@ bool fixup_exception(struct pt_regs *regs, unsigned long esr)
 	case EX_TYPE_UACCESS_ERR_ZERO:
 	case EX_TYPE_KACCESS_ERR_ZERO:
 		return ex_handler_uaccess_err_zero(ex, regs);
+	case EX_TYPE_MMIO_READ_ERR_ZERO:
+		return false;
 	case EX_TYPE_UACCESS_CPY:
 		return ex_handler_uaccess_cpy(ex, regs, esr);
 	case EX_TYPE_LOAD_UNALIGNED_ZEROPAD:
@@ -109,3 +113,19 @@ bool fixup_exception(struct pt_regs *regs, unsigned long esr)
 
 	BUG();
 }
+
+bool fixup_sea_exception(struct pt_regs *regs, unsigned long esr)
+{
+	const struct exception_table_entry *ex;
+
+	if (ESR_ELx_EC(esr) != ESR_ELx_EC_DABT_CUR ||
+	    (esr & ESR_ELx_FSC) != ESR_ELx_FSC_EXTABT ||
+	    (esr & ESR_ELx_WNR))
+		return false;
+
+	ex = search_exception_tables(instruction_pointer(regs));
+	if (!ex || ex->type != EX_TYPE_MMIO_READ_ERR_ZERO)
+		return false;
+
+	return ex_handler_uaccess_err_zero(ex, regs);
+}
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index b227368..ebe8054 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -30,6 +30,7 @@
 #include <linux/hugetlb.h>
 
 #include <asm/acpi.h>
+#include <asm/asm-extable.h>
 #include <asm/bug.h>
 #include <asm/cmpxchg.h>
 #include <asm/cpufeature.h>
@@ -879,6 +880,9 @@ static int do_sea(unsigned long far, unsigned long esr, struct pt_regs *regs)
 	const struct fault_info *inf;
 	unsigned long siaddr;
 
+	if (fixup_sea_exception(regs, esr))
+		return 0;
+
 	inf = esr_to_fault_info(esr);
 
 	if (user_mode(regs) && apei_claim_sea(regs) == 0) {

-- 
Git-155)

[PATCH RFC v2 3/3] PCI: rockchip-host: Recover downstream configuration access

[Matt Thompson via B4 Relay]

From: Matt Thompson <matt@boondocker.io>

The link status can change between the readiness check and a downstream
PCI configuration read. A link that reports up can also fail to return
a usable completion.

On arm64, annotate downstream loads for all three access widths so a
synchronous external abort returns PCIBIOS_DEVICE_NOT_FOUND with all-ones
data. Keep little-endian conversion and I/O read ordering on success.

After retraining, the controller can continue to block configuration
traffic until its AXI link-down latch is cleared. Clear the latch before
downstream config reads and writes once the link readiness checks pass.

Link: https://lore.kernel.org/linux-pci/20261024-rockchip-pcie-resume-v1-2-58e54a5cf5f1@iav.lv/

Signed-off-by: Matt Thompson <matt@boondocker.io>
---
 drivers/pci/controller/pcie-rockchip-host.c | 62 +++++++++++++++++++++++++++--
 drivers/pci/controller/pcie-rockchip.h      |  1 +
 2 files changed, 59 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/controller/pcie-rockchip-host.c b/drivers/pci/controller/pcie-rockchip-host.c
index 35105c1..64ac6f4 100644
--- a/drivers/pci/controller/pcie-rockchip-host.c
+++ b/drivers/pci/controller/pcie-rockchip-host.c
@@ -29,6 +29,10 @@
 #include "../pci.h"
 #include "pcie-rockchip.h"
 
+#ifdef CONFIG_ARM64
+#include <asm/asm-extable.h>
+#endif
+
 static void rockchip_pcie_enable_bw_int(struct rockchip_pcie *rockchip)
 {
 	u32 status;
@@ -149,16 +153,36 @@ static bool rockchip_pcie_downstream_ready(struct rockchip_pcie *rockchip)
 	       PCIE_LINK_TRAINING_DONE(rockchip_pcie_read(rockchip, PCIE_CORE_CTRL));
 }
 
+#ifdef CONFIG_ARM64
+/*
+ * An absent completion can raise a synchronous external abort even when
+ * the link status indicated up immediately before the config transaction.
+ */
+#define rockchip_pcie_cfg_load(insn, addr, val)			\
+	({								\
+		int err = 0;					\
+		asm volatile("1: " #insn " %w0, [%2]\n"			\
+			     "2:\n"					\
+			     _ASM_EXTABLE_MMIO_READ_ERR_ZERO(1b, 2b,	\
+							    %w1, %w0)	\
+			     : "=&r" (val), "+r" (err)			\
+			     : "r" (addr) : "memory");			\
+		err;							\
+	})
+#endif
+
 static int rockchip_pcie_rd_other_conf(struct rockchip_pcie *rockchip,
 				       struct pci_bus *bus, u32 devfn,
 				       int where, int size, u32 *val)
 {
 	void __iomem *addr;
+#ifdef CONFIG_ARM64
+	u32 data;
+	int err;
+#endif
 
-	if (!rockchip_pcie_downstream_ready(rockchip)) {
-		*val = ~0U;
-		return PCIBIOS_DEVICE_NOT_FOUND;
-	}
+	if (!rockchip_pcie_downstream_ready(rockchip))
+		goto absent;
 
 	addr = rockchip->reg_base + PCIE_ECAM_OFFSET(bus->number, devfn, where);
 
@@ -174,6 +198,28 @@ static int rockchip_pcie_rd_other_conf(struct rockchip_pcie *rockchip,
 		rockchip_pcie_cfg_configuration_accesses(rockchip,
 						AXI_WRAPPER_TYPE1_CFG);
 
+	/* Clear the AXI link-down latch before downstream config traffic. */
+	rockchip_pcie_write(rockchip, 0, PCIE_CORE_AXI_LINK_DOWN);
+
+#ifdef CONFIG_ARM64
+	if (size == 4) {
+		err = rockchip_pcie_cfg_load(ldr, addr, data);
+		*val = le32_to_cpu((__force __le32)data);
+	} else if (size == 2) {
+		err = rockchip_pcie_cfg_load(ldrh, addr, data);
+		*val = le16_to_cpu((__force __le16)data);
+	} else if (size == 1) {
+		err = rockchip_pcie_cfg_load(ldrb, addr, data);
+		*val = data;
+	} else {
+		*val = 0;
+		return PCIBIOS_BAD_REGISTER_NUMBER;
+	}
+	if (err)
+		goto absent;
+	/* Preserve the I/O read ordering of readl/readw/readb. */
+	__io_ar(*val);
+#else
 	if (size == 4) {
 		*val = readl(addr);
 	} else if (size == 2) {
@@ -184,7 +230,12 @@ static int rockchip_pcie_rd_other_conf(struct rockchip_pcie *rockchip,
 		*val = 0;
 		return PCIBIOS_BAD_REGISTER_NUMBER;
 	}
+#endif
 	return PCIBIOS_SUCCESSFUL;
+
+absent:
+	*val = ~0U;
+	return PCIBIOS_DEVICE_NOT_FOUND;
 }
 
 static int rockchip_pcie_wr_other_conf(struct rockchip_pcie *rockchip,
@@ -208,6 +259,9 @@ static int rockchip_pcie_wr_other_conf(struct rockchip_pcie *rockchip,
 		rockchip_pcie_cfg_configuration_accesses(rockchip,
 						AXI_WRAPPER_TYPE1_CFG);
 
+	/* Clear the AXI link-down latch before downstream config traffic. */
+	rockchip_pcie_write(rockchip, 0, PCIE_CORE_AXI_LINK_DOWN);
+
 	if (size == 4)
 		writel(val, addr);
 	else if (size == 2)
diff --git a/drivers/pci/controller/pcie-rockchip.h b/drivers/pci/controller/pcie-rockchip.h
index b5da156..1cc3621 100644
--- a/drivers/pci/controller/pcie-rockchip.h
+++ b/drivers/pci/controller/pcie-rockchip.h
@@ -164,6 +164,7 @@
 #define MIN_AXI_ADDR_BITS_PASSED		8
 #define PCIE_ADDR_MASK			GENMASK_ULL(63, MIN_AXI_ADDR_BITS_PASSED)
 #define PCIE_CORE_AXI_CONF_BASE		0xc00000
+#define PCIE_CORE_AXI_LINK_DOWN		(PCIE_CORE_AXI_CONF_BASE + 0x824)
 #define PCIE_CORE_OB_REGION_ADDR0	(PCIE_CORE_AXI_CONF_BASE + 0x0)
 #define   PCIE_CORE_OB_REGION_ADDR0_NUM_BITS	0x3f
 #define   PCIE_CORE_OB_REGION_ADDR0_LO_ADDR	PCIE_ADDR_MASK

-- 
Git-155)

Re: [PATCH RFC v2 3/3] PCI: rockchip-host: Recover downstream configuration access

[sashiko-bot]

> From: Matt Thompson <matt@boondocker.io>
> 
> The link status can change between the readiness check and a downstream
> PCI configuration read. A link that reports up can also fail to return
> a usable completion.
> 
> On arm64, annotate downstream loads for all three access widths so a
> synchronous external abort returns PCIBIOS_DEVICE_NOT_FOUND with all-ones
> data. Keep little-endian conversion and I/O read ordering on success.
> 
> After retraining, the controller can continue to block configuration
> traffic until its AXI link-down latch is cleared. Clear the latch before
> downstream config reads and writes once the link readiness checks pass.
> 
> Link: https://lore.kernel.org/linux-pci/20261024-rockchip-pcie-resume-v1-2-58e54a5cf5f1@iav.lv/
> 
> Signed-off-by: Matt Thompson <matt@boondocker.io>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261113-rfc-b4-v2-0-d6b14f95c1d6@boondocker.io?part=3

Re: [PATCH RFC v2 2/3] arm64: Allow synchronous abort fixups for guarded MMIO reads

[sashiko-bot]

> From: Matt Thompson <matt@boondocker.io>
> 
> An RK3399 PCI configuration read can raise a synchronous external data
> abort if it does not get a usable response. Allow an explicitly annotated
> MMIO load to return an error in this case.
> 
> Match only a current-EL synchronous external abort on a read instruction
> with the new exception table type. Keep existing handling for other
> faults, including asynchronous SError and translation table walk aborts.
> 
> Signed-off-by: Matt Thompson <matt@boondocker.io>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261113-rfc-b4-v2-0-d6b14f95c1d6@boondocker.io?part=2

Re: [PATCH RFC v2 1/3] PCI: rockchip-host: Skip downstream config access while link is down

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] PCI: rockchip-host: missing Fixes trailer for link-down config
  access fix
--

commit 776ef94e954858f6a44d96ce2b3db1d4c94ca081
Author: Matt Thompson <matt@boondocker.io>

> PCI: rockchip-host: Skip downstream config access while link is down
>
> On a RockPro64, a PCI bus rescan with the downstream FPGA unavailable
> faulted in rockchip_pcie_rd_conf() during a vendor ID read. The rescan
> task exited with interrupts disabled and the watchdog reported a lockup.
>
> Check the controller's link-up and link-training status before issuing
> downstream config requests. Return PCIBIOS_DEVICE_NOT_FOUND while the
> link is unavailable. Root port config access still uses the local
> controller registers.
>
> This check cannot prevent the link from dropping during the transaction.
>
> Signed-off-by: Matt Thompson <matt@boondocker.io>

[Severity: Low]
This fixes a kernel fault when rockchip_pcie_rd_other_conf() or
rockchip_pcie_wr_other_conf() issues a downstream config access while the
link is down.  Should this include:

  Fixes: e77f847df54c ("PCI: rockchip: Add Rockchip PCIe controller support")

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261113-rfc-b4-v2-0-d6b14f95c1d6@boondocker.io?part=1