[acpi] Generalise DSDT/SSDT data extraction logic

Allow for the DSDT/SSDT signature-scanning and value extraction code
to be reused for extracting a pass-through MAC address.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/interface/pcbios/acpipwr.c

@@ -42,6 +42,69 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 /** _S5_ signature */
 #define S5_SIGNATURE ACPI_SIGNATURE ( '_', 'S', '5', '_' )
 
+/**
+ * Extract \_Sx value from DSDT/SSDT
+ *
+ * @v zsdt		DSDT or SSDT
+ * @v len		Length of DSDT/SSDT
+ * @v offset		Offset of signature within DSDT/SSDT
+ * @v data		Data buffer
+ * @ret rc		Return status code
+ *
+ * In theory, extracting the \_Sx value from the DSDT/SSDT requires a
+ * full ACPI parser plus some heuristics to work around the various
+ * broken encodings encountered in real ACPI implementations.
+ *
+ * In practice, we can get the same result by scanning through the
+ * DSDT/SSDT for the signature (e.g. "_S5_"), extracting the first
+ * four bytes, removing any bytes with bit 3 set, and treating
+ * whatever is left as a little-endian value.  This is one of the
+ * uglier hacks I have ever implemented, but it's still prettier than
+ * the ACPI specification itself.
+ */
+static int acpi_extract_sx ( userptr_t zsdt, size_t len, size_t offset,
+			     void *data ) {
+	unsigned int *sx = data;
+	uint8_t bytes[4];
+	uint8_t *byte;
+
+	/* Skip signature and package header */
+	offset += ( 4 /* signature */ + 3 /* package header */ );
+
+	/* Sanity check */
+	if ( ( offset + sizeof ( bytes ) /* value */ ) > len ) {
+		return -EINVAL;
+	}
+
+	/* Read first four bytes of value */
+	copy_from_user ( bytes, zsdt, offset, sizeof ( bytes ) );
+	DBGC ( colour, "ACPI found \\_Sx containing %02x:%02x:%02x:%02x\n",
+	       bytes[0], bytes[1], bytes[2], bytes[3] );
+
+	/* Extract \Sx value.  There are three potential encodings
+	 * that we might encounter:
+	 *
+	 * - SLP_TYPa, SLP_TYPb, rsvd, rsvd
+	 *
+	 * - <byteprefix>, SLP_TYPa, <byteprefix>, SLP_TYPb, ...
+	 *
+	 * - <dwordprefix>, SLP_TYPa, SLP_TYPb, 0, 0
+	 *
+	 * Since <byteprefix> and <dwordprefix> both have bit 3 set,
+	 * and valid SLP_TYPx must have bit 3 clear (since SLP_TYPx is
+	 * a 3-bit field), we can just skip any bytes with bit 3 set.
+	 */
+	byte = bytes;
+	if ( *byte & 0x08 )
+		byte++;
+	*sx = *(byte++);
+	if ( *byte & 0x08 )
+		byte++;
+	*sx |= ( *byte << 8 );
+
+	return 0;
+}
+
 /**
  * Power off the computer using ACPI
  *
@@ -56,7 +119,7 @@ int acpi_poweroff ( void ) {
 	unsigned int pm1b_cnt;
 	unsigned int slp_typa;
 	unsigned int slp_typb;
-	int s5;
+	unsigned int s5;
 	int rc;
 
 	/* Locate FADT */
@@ -74,9 +137,8 @@ int acpi_poweroff ( void ) {
 	pm1b_cnt = ( pm1b_cnt_blk + ACPI_PM1_CNT );
 
 	/* Extract \_S5 from DSDT or any SSDT */
-	s5 = acpi_sx ( S5_SIGNATURE );
+	if ( ( rc = acpi_extract ( S5_SIGNATURE, &s5,
-	if ( s5 < 0 ) {
+				   acpi_extract_sx ) ) != 0 ) {
-		rc = s5;
 		DBGC ( colour, "ACPI could not extract \\_S5: %s\n",
 		       strerror ( rc ) );
 		return rc;

src/core/acpi.c

@@ -169,33 +169,22 @@ userptr_t acpi_find_via_rsdt ( uint32_t signature, unsigned int index ) {
 }
 
 /**
- * Extract \_Sx value from DSDT/SSDT
+ * Extract value from DSDT/SSDT
  *
  * @v zsdt		DSDT or SSDT
  * @v signature		Signature (e.g. "_S5_")
- * @ret sx		\_Sx value, or negative error
+ * @v data		Data buffer
- *
+ * @v extract		Extraction method
- * In theory, extracting the \_Sx value from the DSDT/SSDT requires a
+ * @ret rc		Return status code
- * full ACPI parser plus some heuristics to work around the various
- * broken encodings encountered in real ACPI implementations.
- *
- * In practice, we can get the same result by scanning through the
- * DSDT/SSDT for the signature (e.g. "_S5_"), extracting the first
- * four bytes, removing any bytes with bit 3 set, and treating
- * whatever is left as a little-endian value.  This is one of the
- * uglier hacks I have ever implemented, but it's still prettier than
- * the ACPI specification itself.
  */
-static int acpi_sx_zsdt ( userptr_t zsdt, uint32_t signature ) {
+static int acpi_zsdt ( userptr_t zsdt, uint32_t signature, void *data,
+		       int ( * extract ) ( userptr_t zsdt, size_t len,
+					   size_t offset, void *data ) ) {
 	struct acpi_header acpi;
-	union {
+	uint32_t buf;
-		uint32_t dword;
-		uint8_t byte[4];
-	} buf;
 	size_t offset;
 	size_t len;
-	unsigned int sx;
+	int rc;
-	uint8_t *byte;
 
 	/* Read table header */
 	copy_from_user ( &acpi, zsdt, 0, sizeof ( acpi ) );
@@ -203,75 +192,51 @@ static int acpi_sx_zsdt ( userptr_t zsdt, uint32_t signature ) {
 
 	/* Locate signature */
 	for ( offset = sizeof ( acpi ) ;
-	      ( ( offset + sizeof ( buf ) /* signature */ + 3 /* pkg header */
+	      ( ( offset + sizeof ( buf ) /* signature */ ) < len ) ;
-		  + sizeof ( buf ) /* value */ ) < len ) ;
 	      offset++ ) {
 
 		/* Check signature */
 		copy_from_user ( &buf, zsdt, offset, sizeof ( buf ) );
-		if ( buf.dword != cpu_to_le32 ( signature ) )
+		if ( buf != cpu_to_le32 ( signature ) )
 			continue;
 		DBGC ( zsdt, "DSDT/SSDT %#08lx found %s at offset %#zx\n",
 		       user_to_phys ( zsdt, 0 ), acpi_name ( signature ),
 		       offset );
-		offset += sizeof ( buf );
 
-		/* Read first four bytes of value */
+		/* Attempt to extract data */
-		copy_from_user ( &buf, zsdt, ( offset + 3 /* pkg header */ ),
+		if ( ( rc = extract ( zsdt, len, offset, data ) ) == 0 )
-				 sizeof ( buf ) );
+			return 0;
-		DBGC ( zsdt, "DSDT/SSDT %#08lx found %s containing "
-		       "%02x:%02x:%02x:%02x\n", user_to_phys ( zsdt, 0 ),
-		       acpi_name ( signature ), buf.byte[0], buf.byte[1],
-		       buf.byte[2], buf.byte[3] );
-
-		/* Extract \Sx value.  There are three potential
-		 * encodings that we might encounter:
-		 *
-		 * - SLP_TYPa, SLP_TYPb, rsvd, rsvd
-		 *
-		 * - <byteprefix>, SLP_TYPa, <byteprefix>, SLP_TYPb, ...
-		 *
-		 * - <dwordprefix>, SLP_TYPa, SLP_TYPb, 0, 0
-		 *
-		 * Since <byteprefix> and <dwordprefix> both have bit
-		 * 3 set, and valid SLP_TYPx must have bit 3 clear
-		 * (since SLP_TYPx is a 3-bit field), we can just skip
-		 * any bytes with bit 3 set.
-		 */
-		byte = &buf.byte[0];
-		if ( *byte & 0x08 )
-			byte++;
-		sx = *(byte++);
-		if ( *byte & 0x08 )
-			byte++;
-		sx |= ( *byte << 8 );
-		return sx;
 	}
 
 	return -ENOENT;
 }
 
 /**
- * Extract \_Sx value from DSDT/SSDT
+ * Extract value from DSDT/SSDT
  *
  * @v signature		Signature (e.g. "_S5_")
- * @ret sx		\_Sx value, or negative error
+ * @v data		Data buffer
+ * @v extract		Extraction method
+ * @ret rc		Return status code
  */
-int acpi_sx ( uint32_t signature ) {
+int acpi_extract ( uint32_t signature, void *data,
+		   int ( * extract ) ( userptr_t zsdt, size_t len,
+				       size_t offset, void *data ) ) {
 	struct acpi_fadt fadtab;
 	userptr_t fadt;
 	userptr_t dsdt;
 	userptr_t ssdt;
 	unsigned int i;
-	int sx;
+	int rc;
 
 	/* Try DSDT first */
 	fadt = acpi_find ( FADT_SIGNATURE, 0 );
 	if ( fadt ) {
 		copy_from_user ( &fadtab, fadt, 0, sizeof ( fadtab ) );
 		dsdt = phys_to_user ( fadtab.dsdt );
-		if ( ( sx = acpi_sx_zsdt ( dsdt, signature ) ) >= 0 )
+		if ( ( rc = acpi_zsdt ( dsdt, signature, data,
-			return sx;
+					extract ) ) == 0 )
+			return 0;
 	}
 
 	/* Try all SSDTs */
@@ -279,11 +244,12 @@ int acpi_sx ( uint32_t signature ) {
 		ssdt = acpi_find ( SSDT_SIGNATURE, i );
 		if ( ! ssdt )
 			break;
-		if ( ( sx = acpi_sx_zsdt ( ssdt, signature ) ) >= 0 )
+		if ( ( rc = acpi_zsdt ( ssdt, signature, data,
-			return sx;
+					extract ) ) == 0 )
+			return 0;
 	}
 
-	DBGC ( colour, "ACPI could not find \\_Sx \"%s\"\n",
+	DBGC ( colour, "ACPI could not find \"%s\"\n",
 	       acpi_name ( signature ) );
 	return -ENOENT;
 }

src/include/ipxe/acpi.h

@@ -387,7 +387,9 @@ acpi_describe ( struct interface *interface );
 	typeof ( struct acpi_descriptor * ( object_type ) )
 
 extern void acpi_fix_checksum ( struct acpi_header *acpi );
-extern int acpi_sx ( uint32_t signature );
+extern int acpi_extract ( uint32_t signature, void *data,
+			  int ( * extract ) ( userptr_t zsdt, size_t len,
+					      size_t offset, void *data ) );
 extern void acpi_add ( struct acpi_descriptor *desc );
 extern void acpi_del ( struct acpi_descriptor *desc );
 extern int acpi_install ( int ( * install ) ( struct acpi_header *acpi ) );