acpigen: Add function to generate unicode names

The ACPI spec 6.3 chapter 6.1.10 states that _STR has to return a buffer
containing UTF-16 characters.

Add function to generate Unicode names and use it for _STR. It will
replace non-ASCII characters with '?'.

Use the introduced function in IPMI driver.

Fixes ACPI warning shown in fwts.

Change-Id: I16992bd449e3a51f6a8875731cd45a9f43de5c8c
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37789
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/x86/acpigen.c

@@ -199,6 +199,21 @@ void acpigen_write_name_string(const char *name, const char *string)
 	acpigen_write_string(string);
 }
 
+void acpigen_write_name_unicode(const char *name, const char *string)
+{
+	const size_t len = strlen(string) + 1;
+	acpigen_write_name(name);
+	acpigen_emit_byte(BUFFER_OP);
+	acpigen_write_len_f();
+	acpigen_write_integer(len);
+	for (size_t i = 0; i < len; i++) {
+		const char c = string[i];
+		/* Simple ASCII to UTF-16 conversion, replace non ASCII characters */
+		acpigen_emit_word(c >= 0 ? c : '?');
+	}
+	acpigen_pop_len();
+}
+
 void acpigen_emit_stream(const char *data, int size)
 {
 	int i;

src/arch/x86/include/arch/acpigen.h

@@ -309,6 +309,7 @@ void acpigen_write_dword(unsigned int data);
 void acpigen_write_qword(uint64_t data);
 void acpigen_write_integer(uint64_t data);
 void acpigen_write_string(const char *string);
+void acpigen_write_name_unicode(const char *name, const char *string);
 void acpigen_write_name(const char *name);
 void acpigen_write_name_zero(const char *name);
 void acpigen_write_name_one(const char *name);

src/drivers/ipmi/ipmi_kcs_ops.c

@@ -253,7 +253,7 @@ static void ipmi_ssdt(struct device *dev)
 	acpigen_write_scope(scope);
 	acpigen_write_device("SPMI");
 	acpigen_write_name_string("_HID", "IPI0001");
-	acpigen_write_name_string("_STR", "IPMI_KCS");
+	acpigen_write_name_unicode("_STR", "IPMI_KCS");
 	acpigen_write_name_byte("_UID", dev->command);
 	acpigen_write_STA(0xf);
 	acpigen_write_name("_CRS");