[RFC PATCH 2/3] ACPI: PHAT: Add generic helper to parse PHAT records

[K Prateek Nayak <kprateek.nayak@amd.com>]

The ACPI Specification v6.5 [1] under Sec. 5.2.31 "Platform Health
Assessment Table (PHAT)" provides a well defined data format for reset
reason records, including the ones that are vendor specific.

Provide a generic helper to locate the vendor specific records and parse
them into a buffer that can be consumed by the users.

The first user for the interface is added in the subsequent commit with
AMD processors using it to parse the s5_RESET_STATUS from PHAT records.

Make the Kconfig depend on ACPI && CPU_SUP_AMD to prevent the need for
unnecessarily compiling in ACPI PHAT support when not needed.

Link: https://uefi.org/sites/default/files/resources/ACPI_Spec_6_5_Aug29.pdf [1]
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
 drivers/acpi/Kconfig     |  11 ++++
 drivers/acpi/Makefile    |   1 +
 drivers/acpi/acpi_phat.c | 133 +++++++++++++++++++++++++++++++++++++++
 include/linux/acpi.h     |  14 +++++
 4 files changed, 159 insertions(+)
 create mode 100644 drivers/acpi/acpi_phat.c

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index f165d14cf61a..494c757a62d7 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -607,6 +607,17 @@ config ACPI_PRMT
 	  substantially increase computational overhead related to the
 	  initialization of some server systems.
 
+config ACPI_PHAT
+	bool "ACPI PHAT Record parsing support"
+	depends on X86 && ACPI && CPU_SUP_AMD
+	default y
+	help
+	  The Platform Health Assessment Table (PHAT) allows platforms to
+	  expose read-only data for diagnostics and health assessments.
+
+	  Enable this feature to access generic helpers for parsing PHAT
+	  data records.
+
 endif	# ACPI
 
 config X86_PM_TIMER
diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
index d1b0affb844f..d6cf252ca4ea 100644
--- a/drivers/acpi/Makefile
+++ b/drivers/acpi/Makefile
@@ -108,6 +108,7 @@ obj-$(CONFIG_ACPI_SPCR_TABLE)	+= spcr.o
 obj-$(CONFIG_ACPI_DEBUGGER_USER) += acpi_dbg.o
 obj-$(CONFIG_ACPI_PPTT) 	+= pptt.o
 obj-$(CONFIG_ACPI_PFRUT)	+= pfr_update.o pfr_telemetry.o
+obj-$(CONFIG_ACPI_PHAT) 	+= acpi_phat.o
 
 # processor has its own "processor." module_param namespace
 processor-y			:= processor_driver.o processor_thermal.o
diff --git a/drivers/acpi/acpi_phat.c b/drivers/acpi/acpi_phat.c
new file mode 100644
index 000000000000..de612ae018e0
--- /dev/null
+++ b/drivers/acpi/acpi_phat.c
@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Helpers for parsing Platform Health Assessment Table (PHAT) records.
+ */
+#include <linux/kernel.h>
+#include <linux/acpi.h>
+
+#include <acpi/actbl2.h>
+
+/*
+ * __phat_get_firmware_health_data() - Internal helper to locate the
+ * "Reset Reason Health Record" within the Platform Health Assessment
+ * Table (PHAT).
+ *
+ * @table: Pointer to the beginning of PHAT.
+ *
+ * Return: A pointer within the @table if "Reset Reason Health Record"
+ * is found; NULL otherwise.
+ */
+static struct acpi_phat_health_data *
+__phat_get_firmware_health_data(struct acpi_table_phat *table)
+{
+	unsigned int length = table->header.length;
+	void *header = table;
+
+	/* No records. */
+	if (length <= sizeof(struct acpi_table_header))
+		return NULL;
+
+	/*
+	 * Advance to the end of the table header
+	 * where the first record starts.
+	 */
+	header += sizeof(struct acpi_table_header);
+	length -= sizeof(struct acpi_table_header);
+
+	/*
+	 * Search for PHAT firmware health data record header
+	 * with type == ACPI_PHAT_TYPE_FW_HEALTH_DATA.
+	 */
+	while (length) {
+		struct acpi_phat_health_data *data = header;
+
+		if (data->header.type == ACPI_PHAT_TYPE_FW_HEALTH_DATA)
+			return header;
+
+		/* Move to the next header */
+		header += data->header.length;
+		length -= data->header.length;
+	}
+
+	return NULL;
+}
+
+/**
+ * acpi_phat_get_vendor_reset_reason - Find a "Vendor Specific Reset Reason
+ * Entry" with the matching @guid from the "Firmware Health Data Record". If
+ * successfully located, the function will allocate an object of the size
+ * "acpi_phat_vendor_element.length" and return a pointer populated with the
+ * content of the record.
+ *
+ * @guid: The "Vendor Data ID" of the reset reason record.
+ *
+ * Return: A valid pointer to an allocated "acpi_phat_vendor_element" populated
+ * with the data from the record with matching @guid; an ERR_PTR() otherwise if
+ * no matching records were found, or if the element could not be allocated.
+ * If a valid pointer was returned, the user must call
+ * acpi_phat_put_vendor_reset_reason() for the object once done to reclaim the
+ * allocated memory.
+ */
+struct acpi_phat_vendor_element *acpi_phat_get_vendor_reset_reason(guid_t *guid)
+{
+	struct acpi_table_header *phat_tbl __free(acpi_put_table) = NULL;
+	struct acpi_phat_health_data *fw_health_data;
+	struct acpi_phat_device_data *dev_data;
+	acpi_status status;
+	void *data;
+	int i;
+
+	status = acpi_get_table(ACPI_SIG_PHAT, 0, &phat_tbl);
+	if (ACPI_FAILURE(status))
+		return ERR_PTR(-ENODEV);
+
+	fw_health_data =
+		__phat_get_firmware_health_data((struct acpi_table_phat *)phat_tbl);
+	if (!fw_health_data)
+		return ERR_PTR(-ENODEV);
+
+	/* Check if Device-specific data record is present. */
+	if (!fw_health_data->device_specific_offset)
+		return ERR_PTR(-ENODEV);
+
+	dev_data = (void *)fw_health_data + fw_health_data->device_specific_offset;
+	if (!dev_data->vendor_count)
+		return ERR_PTR(-ENODEV);
+
+	/* Vendor data starts after Device-specific data */
+	data = (void *)dev_data + sizeof(*dev_data);
+
+	for (i = 0; i <= dev_data->vendor_count; ++i) {
+		struct acpi_phat_vendor_element *vendor_data = data;
+		int length = vendor_data->length;
+
+		/*
+		 * Move to the next Vendor specific entry if
+		 * the GUID of entry doesn't match.
+		 */
+		if (!guid_equal(guid, (guid_t *)vendor_data->vendor_guid)) {
+			data += vendor_data->length;
+			continue;
+		}
+
+		vendor_data = kmalloc(length, GFP_KERNEL);
+		if (!vendor_data)
+			return ERR_PTR(-ENOMEM);
+
+		memcpy(vendor_data, data, length);
+		return vendor_data;
+	}
+
+	return ERR_PTR(-ENODEV);
+}
+
+/**
+ * acpi_phat_put_vendor_reset_reason - Reclaim the object allocated by
+ * acpi_phat_get_vendor_reset_reason().
+ *
+ * @reason: A valid pointer returned by acpi_phat_get_vendor_reset_reason()
+ */
+void acpi_phat_put_vendor_reset_reason(struct acpi_phat_vendor_element *reason)
+{
+	kfree(reason);
+}
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 67effb91fa98..daed1d66ca43 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1627,6 +1627,20 @@ extern int acpi_ffh_address_space_arch_handler(acpi_integer *value,
 static inline void acpi_init_ffh(void) { }
 #endif
 
+#ifdef CONFIG_ACPI_PHAT
+struct acpi_phat_vendor_element *acpi_phat_get_vendor_reset_reason(guid_t *guid);
+void acpi_phat_put_vendor_reset_reason(struct acpi_phat_vendor_element *reason);
+#else
+static inline struct acpi_phat_vendor_element *
+acpi_phat_get_vendor_reset_reason(guid_t *guid)
+{
+	return ERR_PTR(-ENODEV);
+}
+
+static inline void
+acpi_phat_put_vendor_reset_reason(struct acpi_phat_vendor_element *reason) { }
+#endif
+
 #ifdef CONFIG_ACPI
 extern void acpi_device_notify(struct device *dev);
 extern void acpi_device_notify_remove(struct device *dev);
-- 
2.34.1