cxl: Enumerate feature commands

Add feature commands enumeration code in order to detect and enumerate
the 3 feature related commands "get supported features", "get feature",
and "set feature". The enumeration will help determine whether the driver
can issue any of the 3 commands to the device.

Reviewed-by: Dan Williams <[e-mail]>
Reviewed-by: Li Ming <[e-mail]>
Reviewed-by: Jonathan Cameron <[e-mail]>
Reviewed-by: Davidlohr Bueso <[e-mail]>
Tested-by: Shiju Jose <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Dave Jiang <[e-mail]>

drivers/cxl/core/mbox.c

···
 	return 0;
 }
 
+static int check_features_opcodes(u16 opcode, int *ro_cmds, int *wr_cmds)
+{
+	switch (opcode) {
+	case CXL_MBOX_OP_GET_SUPPORTED_FEATURES:
+	case CXL_MBOX_OP_GET_FEATURE:
+		(*ro_cmds)++;
+		return 1;
+	case CXL_MBOX_OP_SET_FEATURE:
+		(*wr_cmds)++;
+		return 1;
+	default:
+		return 0;
+	}
+}
+
+/* 'Get Supported Features' and 'Get Feature' */
+#define MAX_FEATURES_READ_CMDS	2
+static void set_features_cap(struct cxl_mailbox *cxl_mbox,
+			     int ro_cmds, int wr_cmds)
+{
+	/* Setting up Features capability while walking the CEL */
+	if (ro_cmds == MAX_FEATURES_READ_CMDS) {
+		if (wr_cmds)
+			cxl_mbox->feat_cap = CXL_FEATURES_RW;
+		else
+			cxl_mbox->feat_cap = CXL_FEATURES_RO;
+	}
+}
+
 /**
  * cxl_walk_cel() - Walk through the Command Effects Log.
  * @mds: The driver data for the operation
···
 	struct cxl_cel_entry *cel_entry;
 	const int cel_entries = size / sizeof(*cel_entry);
 	struct device *dev = mds->cxlds.dev;
-	int i;
+	int i, ro_cmds = 0, wr_cmds = 0;
 
 	cel_entry = (struct cxl_cel_entry *) cel;
 
···
 			set_bit(cmd->info.id, cxl_mbox->enabled_cmds);
 			enabled++;
 		}
+
+		enabled += check_features_opcodes(opcode, &ro_cmds,
+						  &wr_cmds);
 
 		if (cxl_is_poison_command(opcode)) {
 			cxl_set_poison_cmd_enabled(&mds->poison, opcode);
···
 		dev_dbg(dev, "Opcode 0x%04x %s\n", opcode,
 			enabled ? "enabled" : "unsupported by driver");
 	}
+
+	set_features_cap(cxl_mbox, ro_cmds, wr_cmds);
 }
 
 static struct cxl_mbox_get_supported_logs *cxl_get_gsl(struct cxl_memdev_state *mds)

drivers/cxl/cxlmem.h

···
 	CXL_MBOX_OP_GET_LOG_CAPS	= 0x0402,
 	CXL_MBOX_OP_CLEAR_LOG           = 0x0403,
 	CXL_MBOX_OP_GET_SUP_LOG_SUBLIST = 0x0405,
+	CXL_MBOX_OP_GET_SUPPORTED_FEATURES	= 0x0500,
+	CXL_MBOX_OP_GET_FEATURE		= 0x0501,
+	CXL_MBOX_OP_SET_FEATURE		= 0x0502,
 	CXL_MBOX_OP_IDENTIFY		= 0x4000,
 	CXL_MBOX_OP_GET_PARTITION_INFO	= 0x4100,
 	CXL_MBOX_OP_SET_PARTITION_INFO	= 0x4101,

include/cxl/features.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright(c) 2024-2025 Intel Corporation. */
+#ifndef __CXL_FEATURES_H__
+#define __CXL_FEATURES_H__
+
+/* Feature commands capability supported by a device */
+enum cxl_features_capability {
+	CXL_FEATURES_NONE = 0,
+	CXL_FEATURES_RO,
+	CXL_FEATURES_RW,
+};
+
+#endif

include/cxl/mailbox.h

···
 #ifndef __CXL_MBOX_H__
 #define __CXL_MBOX_H__
 #include <linux/rcuwait.h>
+#include <cxl/features.h>
 #include <uapi/linux/cxl_mem.h>
 
 /**
···
  * @mbox_mutex: mutex protects device mailbox and firmware
  * @mbox_wait: rcuwait for mailbox
  * @mbox_send: @dev specific transport for transmitting mailbox commands
+ * @feat_cap: Features capability
  */
 struct cxl_mailbox {
 	struct device *host;
···
 	struct mutex mbox_mutex; /* lock to protect mailbox context */
 	struct rcuwait mbox_wait;
 	int (*mbox_send)(struct cxl_mailbox *cxl_mbox, struct cxl_mbox_cmd *cmd);
+	enum cxl_features_capability feat_cap;
 };
 
 int cxl_mailbox_init(struct cxl_mailbox *cxl_mbox, struct device *host);