ACPI: APEI: GHES: Add helper for CPER CXL protocol errors checks

Move the CPER CXL protocol errors validity check out of
cxl_cper_post_prot_err() to new cxl_cper_sec_prot_err_valid() and limit
the serial number check only to CXL agents that are CXL devices (UEFI
v2.10, Appendix N.2.13).

Export the new symbol for reuse by ELOG.

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
[ rjw: Subject tweak ]
Link: https://patch.msgid.link/20260114101543.85926-4-fabio.m.de.francesco@linux.intel.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: fdefranc

drivers/acpi/apei/Makefile

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_ACPI_APEI)		+= apei.o
 obj-$(CONFIG_ACPI_APEI_GHES)	+= ghes.o
+obj-$(CONFIG_ACPI_APEI_PCIEAER)	+= ghes_helpers.o
 obj-$(CONFIG_ACPI_APEI_EINJ)	+= einj.o
 einj-y				:= einj-core.o
 einj-$(CONFIG_ACPI_APEI_EINJ_CXL) += einj-cxl.o

drivers/acpi/apei/ghes.c

@@ -741,24 +741,8 @@ static void cxl_cper_post_prot_err(struct cxl_cper_sec_prot_err *prot_err,
 	struct cxl_cper_prot_err_work_data wd;
 	u8 *dvsec_start, *cap_start;
 
-	if (!(prot_err->valid_bits & PROT_ERR_VALID_AGENT_ADDRESS)) {
-		pr_err_ratelimited("CXL CPER invalid agent type\n");
+	if (cxl_cper_sec_prot_err_valid(prot_err))
 		return;
-	}
-
-	if (!(prot_err->valid_bits & PROT_ERR_VALID_ERROR_LOG)) {
-		pr_err_ratelimited("CXL CPER invalid protocol error log\n");
-		return;
-	}
-
-	if (prot_err->err_len != sizeof(struct cxl_ras_capability_regs)) {
-		pr_err_ratelimited("CXL CPER invalid RAS Cap size (%u)\n",
-				   prot_err->err_len);
-		return;
-	}
-
-	if (!(prot_err->valid_bits & PROT_ERR_VALID_SERIAL_NUMBER))
-		pr_warn(FW_WARN "CXL CPER no device serial number\n");
 
 	guard(spinlock_irqsave)(&cxl_cper_prot_err_work_lock);
 

drivers/acpi/apei/ghes_helpers.c

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright(c) 2025 Intel Corporation. All rights reserved
+
+#include <linux/printk.h>
+#include <cxl/event.h>
+
+int cxl_cper_sec_prot_err_valid(struct cxl_cper_sec_prot_err *prot_err)
+{
+	if (!(prot_err->valid_bits & PROT_ERR_VALID_AGENT_ADDRESS)) {
+		pr_err_ratelimited("CXL CPER invalid agent type\n");
+		return -EINVAL;
+	}
+
+	if (!(prot_err->valid_bits & PROT_ERR_VALID_ERROR_LOG)) {
+		pr_err_ratelimited("CXL CPER invalid protocol error log\n");
+		return -EINVAL;
+	}
+
+	if (prot_err->err_len != sizeof(struct cxl_ras_capability_regs)) {
+		pr_err_ratelimited("CXL CPER invalid RAS Cap size (%u)\n",
+				   prot_err->err_len);
+		return -EINVAL;
+	}
+
+	if ((prot_err->agent_type == RCD || prot_err->agent_type == DEVICE ||
+	     prot_err->agent_type == LD || prot_err->agent_type == FMLD) &&
+	    !(prot_err->valid_bits & PROT_ERR_VALID_SERIAL_NUMBER))
+		pr_warn_ratelimited(FW_WARN
+				    "CXL CPER no device serial number\n");
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(cxl_cper_sec_prot_err_valid);

include/cxl/event.h

@@ -320,4 +320,14 @@ static inline int cxl_cper_prot_err_kfifo_get(struct cxl_cper_prot_err_work_data
 }
 #endif
 
+#ifdef CONFIG_ACPI_APEI_PCIEAER
+int cxl_cper_sec_prot_err_valid(struct cxl_cper_sec_prot_err *prot_err);
+#else
+static inline int
+cxl_cper_sec_prot_err_valid(struct cxl_cper_sec_prot_err *prot_err)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
 #endif /* _LINUX_CXL_EVENT_H */