drm/apple: Add bounded firmware-27 AFK framing

drivers/gpu/drm/apple/afk-v2.h

@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright 2026 Aurora Silicon */
+
+#ifndef APPLE_AFK_V2_H
+#define APPLE_AFK_V2_H
+
+#include <linux/errno.h>
+#include <linux/types.h>
+#include <linux/unaligned.h>
+
+struct epic_hdr_v2 {
+	u8 seq;
+	u8 flags;
+	__le16 channel;
+	__le32 length; /* bytes after the first eight transport bytes */
+	__le64 timestamp;
+	u8 type;
+	u8 category; /* report=0, command=1, reply=2 */
+	__le16 interface_flags;
+	__le32 reserved;
+} __packed;
+
+struct epic_cmd_v2 {
+	u8 flags; /* bit 0: out-of-band buffer descriptors follow */
+	u8 tag;
+	__le16 reserved;
+	__le32 length; /* command: response capacity; reply: status */
+	__le64 rxbuf;
+	__le64 txbuf;
+	__le32 rxlen;
+	__le32 txlen;
+} __packed;
+
+/* length excludes the first eight transport bytes. Ignore ring padding. */
+static inline int afk_v2_payload_size(const struct epic_hdr_v2 *header,
+				      size_t record_size, size_t *payload_size)
+{
+	u32 length;
+
+	if (record_size < sizeof(*header) || header->category > 2)
+		return -EINVAL;
+	length = le32_to_cpu(header->length);
+	if (length < sizeof(*header) - 8 || length > record_size - 8)
+		return -EINVAL;
+	*payload_size = length - (sizeof(*header) - 8);
+	return 0;
+}
+
+static inline u16 afk_command_tag(bool v2, u8 generation, unsigned int slot)
+{
+	return v2 ? (((generation & 0xf) << 4) | slot) :
+		     (((u16)generation << 8) | slot);
+}
+
+static inline unsigned int afk_command_slot(bool v2, u16 tag)
+{
+	return tag & (v2 ? 0xf : 0xff);
+}
+
+#endif