[PATCH v20 5/9] cxl: Update CXL Endpoint AER handler

[Terry Bowman <terry.bowman@amd.com>]

Rename cxl_error_detected() to cxl_pci_error_detected() and rename the
struct pci_error_handlers instance from cxl_error_handlers to
cxl_pci_error_handlers for consistency with the cxl_pci_ prefix used by
the renamed handler and the rest of the PCI-facing entry points.

Document the unconditional CXL RAS read policy: on a dead link, readl()
returns 0xFFFFFFFF which is interpreted as UCE bits set and triggers a
panic. If RAS registers are not mapped the read is skipped and the
frozen/perm_failure switch cases defer to AER recovery for devices
without active CXL.mem traffic.

Signed-off-by: Terry Bowman <terry.bowman@amd.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>

---

Changes in v19->v20:
- Expand the comment block in cxl_pci_error_detected().
- Clarify commit message's first paragraph. cxl_error_handlers is a variable
- Clarify AER handling in cxl_pci_error_detected() block comment

Changes in v18->v19:
- Add review-by for DaveJ and Jonathan
- Remove reindent introduced in v18 at cxl_error_handlers definition.

Changes in v17->v18:
- Fix cxl_pci_error_detected() to use find_cxl_port_by_uport() and port->uport_dev
- Read CXL RAS unconditionally; panic on UCE regardless of channel state
- Document unconditional read policy and 0xFFFFFFFF behavior in comment
- Drop guard removal paragraph from commit message (not in this diff)
- Drop Reviewed-by tags pending re-review after message change

Changes in v16->v17:
- Rename pci_error_handlers struct instance to cxl_pci_error_handlers for
  cxl_pci_ naming consistency.
- Restore scoped_guard(device) and dev->driver check around AER read.
- NULL-check find_cxl_port_by_dev() before deref of port->uport_dev.
- Updated commit message. (Terry)
- Add scope cleanup for port variable in cxl_pci_error_detected() (Terry)
- Drop cxl_uncor_aer_present(), rely on AER state

Changes in v15->v16:
- Update commit message (DaveJ)
- s/cxl_handle_aer()/cxl_uncor_aer_present()/g (Jonathan)
- cxl_uncor_aer_present(): Leave original result calculation based on
  if a UCE is present and the provided state (Terry)
- Add call to pci_print_aer(). AER fails to log because is upstream
  link (Terry)

Changes in v14->v15:
- Update commit message and title. Added Bjorn's ack.
- Move CE and UCE handling logic here

Changes in v13->v14:
- Add Dave Jiang's review-by
- Update commit message & headline (Bjorn)
- Refactor cxl_port_error_detected()/cxl_port_cor_error_detected() to
  one line (Jonathan)
- Remove cxl_walk_port() (Dan)
- Remove cxl_pci_drv_bound(). Check for 'is_cxl' parent port is
  sufficient (Dan)
- Remove device_lock_if()
- Combined CE and UCE here (Terry)

Changes in v12->v13:
- Move get_pci_cxl_host_dev() and cxl_handle_proto_error() to Dequeue
  patch (Terry)
- Remove EP case in cxl_get_ras_base(), not used. (Terry)
- Remove check for dport->dport_dev (Dave)
- Remove whitespace (Terry)

Changes in v11->v12:
- Add call to cxl_pci_drv_bound() in cxl_handle_proto_error() and
  pci_to_cxl_dev()
- Change cxl_error_detected() -> cxl_cor_error_detected()
- Remove NULL variable assignments
- Replace bus_find_device() with find_cxl_port_by_uport() for upstream
  port searches.

Changes in v10->v11:
- None
---
 drivers/cxl/core/ras.c | 25 ++++++++++++++++---------
 drivers/cxl/cxlpci.h   |  8 ++++----
 drivers/cxl/pci.c      |  6 +++---
 3 files changed, 23 insertions(+), 16 deletions(-)

diff --git a/drivers/cxl/core/ras.c b/drivers/cxl/core/ras.c
index e99dcd028b738..bf479fac08565 100644
--- a/drivers/cxl/core/ras.c
+++ b/drivers/cxl/core/ras.c
@@ -61,7 +61,7 @@ cxl_cper_trace_uncorr_prot_err(struct cxl_memdev *cxlmd,
 
 	/*
 	 * ras_cap.header_log[] holds CXL_HEADERLOG_SIZE_U32 (16) hardware
-	 * dwords.  Copy them into the front of a zero-filled
+	 * dwords. Copy them into the front of a zero-filled
 	 * CXL_HEADERLOG_TRACE_SIZE_U32 (128) u32 staging buffer so the trace
 	 * event memcpy sees a full 512-byte source and the userspace ABI
 	 * (rasdaemon) is preserved.
@@ -320,8 +320,8 @@ bool cxl_handle_ras(struct cxl_port *port, struct cxl_dport *dport, void __iomem
 	return true;
 }
 
-pci_ers_result_t cxl_error_detected(struct pci_dev *pdev,
-				    pci_channel_state_t state)
+pci_ers_result_t cxl_pci_error_detected(struct pci_dev *pdev,
+					pci_channel_state_t state)
 {
 	struct cxl_port *port __free(put_cxl_port) = find_cxl_port_by_uport(&pdev->dev);
 	bool ue = false;
@@ -341,11 +341,18 @@ pci_ers_result_t cxl_error_detected(struct pci_dev *pdev,
 		}
 
 		/*
-		 * The CXL RAS read is unconditional regardless of channel
-		 * state. Any uncorrectable error bit set in the CXL RAS
-		 * status register triggers a panic below because CXL.mem
-		 * cache coherency is already lost; continuing risks silent
-		 * data corruption.
+		 * The CXL RAS uncorrectable status is the only signal here
+		 * that the error is a CXL internal (protocol) error. A set
+		 * UCE bit confirms it and triggers the panic below. On a dead
+		 * link readl() returns 0xFFFFFFFF, which sets all UCE bits and
+		 * triggers the panic intentionally.
+		 *
+		 * If RAS is not mapped the read is skipped. Unlike
+		 * cxl_do_recovery(), which is reached only after
+		 * is_aer_internal_error() has already confirmed a CXL internal
+		 * UCE, this path has no such confirmation, so an unmapped RAS
+		 * block cannot attribute the error to CXL and must not panic.
+		 * The switch cases below then handle AER recovery.
 		 */
 		ue = cxl_handle_ras(port, NULL, to_ras_base(port, NULL));
 	}
@@ -373,7 +380,7 @@ pci_ers_result_t cxl_error_detected(struct pci_dev *pdev,
 	}
 	return PCI_ERS_RESULT_NEED_RESET;
 }
-EXPORT_SYMBOL_NS_GPL(cxl_error_detected, "CXL");
+EXPORT_SYMBOL_NS_GPL(cxl_pci_error_detected, "CXL");
 
 static void cxl_handle_proto_error(struct pci_dev *pdev, struct cxl_port *port,
 				   struct cxl_dport *dport, int severity)
diff --git a/drivers/cxl/cxlpci.h b/drivers/cxl/cxlpci.h
index 606fadd2476f3..7421132899fc4 100644
--- a/drivers/cxl/cxlpci.h
+++ b/drivers/cxl/cxlpci.h
@@ -79,13 +79,13 @@ struct cxl_dev_state;
 void read_cdat_data(struct cxl_port *port);
 
 #ifdef CONFIG_CXL_RAS
-pci_ers_result_t cxl_error_detected(struct pci_dev *pdev,
-				    pci_channel_state_t state);
+pci_ers_result_t cxl_pci_error_detected(struct pci_dev *pdev,
+					pci_channel_state_t state);
 void devm_cxl_dport_rch_ras_setup(struct cxl_dport *dport);
 void devm_cxl_port_ras_setup(struct cxl_port *port);
 #else
-static inline pci_ers_result_t cxl_error_detected(struct pci_dev *pdev,
-						  pci_channel_state_t state)
+static inline pci_ers_result_t cxl_pci_error_detected(struct pci_dev *pdev,
+						      pci_channel_state_t state)
 {
 	return PCI_ERS_RESULT_NONE;
 }
diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
index fe11be7fd9aab..1e7be77ded634 100644
--- a/drivers/cxl/pci.c
+++ b/drivers/cxl/pci.c
@@ -998,8 +998,8 @@ static void cxl_reset_done(struct pci_dev *pdev)
 	}
 }
 
-static const struct pci_error_handlers cxl_error_handlers = {
-	.error_detected	= cxl_error_detected,
+static const struct pci_error_handlers cxl_pci_error_handlers = {
+	.error_detected	= cxl_pci_error_detected,
 	.slot_reset	= cxl_slot_reset,
 	.resume		= cxl_error_resume,
 	.reset_done	= cxl_reset_done,
@@ -1009,7 +1009,7 @@ static struct pci_driver cxl_pci_driver = {
 	.name			= KBUILD_MODNAME,
 	.id_table		= cxl_mem_pci_tbl,
 	.probe			= cxl_pci_probe,
-	.err_handler		= &cxl_error_handlers,
+	.err_handler		= &cxl_pci_error_handlers,
 	.dev_groups		= cxl_rcd_groups,
 	.driver	= {
 		.probe_type	= PROBE_PREFER_ASYNCHRONOUS,
-- 
2.34.1