lib: Introduce fw_config_get_field

In some cases, fw_config is used for ids like sar_id, sku_id etc.
To avoid calling fw_config_probe over and over, hence provide the
method to return the value then caller can use the switch case
instead of if else statement.

TEST=get fw_config field value on nivviks.
[INFO ]  fw_config get field name=DB_USB, mask=0x3, shift=0, value =0x1

Signed-off-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Change-Id: Iae89668e8fe7322d5a4dcbf88a97d7ed36619af5
Reviewed-on: https://review.coreboot.org/c/coreboot/+/70745
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Tim Wawrzynczak <inforichland@gmail.com>

src/include/fw_config.h

@@ -24,6 +24,11 @@ struct fw_config {
 	uint64_t value;
 };
 
+struct fw_config_field {
+	const char *field_name;
+	uint64_t mask;
+};
+
 /* Generate a pointer to a compound literal of the fw_config structure. */
 #define FW_CONFIG(__field, __option)	(&(const struct fw_config) {		\
 	.field_name = FW_CONFIG_FIELD_##__field##_NAME,				\
@@ -32,6 +37,11 @@ struct fw_config {
 	.value = FW_CONFIG_FIELD_##__field##_OPTION_##__option##_VALUE		\
 })
 
+#define FW_CONFIG_FIELD(__field) (&(const struct fw_config_field) {		\
+	.field_name = FW_CONFIG_FIELD_##__field##_NAME,				\
+	.mask = FW_CONFIG_FIELD_##__field##_MASK,				\
+})
+
 /**
  * fw_config_get() - Provide firmware configuration value.
  *
@@ -41,6 +51,16 @@ uint64_t fw_config_get(void);
 
 #if CONFIG(FW_CONFIG)
 
+/**
+ * fw_config_get_field() - Provide firmware configuration field value.
+ * @field: Structure containing field name and mask
+ *
+ * Return 64bit firmware configuration value determined for the system.
+ * Will return UNDEFINED_FW_CONFIG if unprovisioned, caller should treat
+ * as error value for the case.
+ */
+uint64_t fw_config_get_field(const struct fw_config_field *field);
+
 /**
  * fw_config_probe() - Check if field and option matches.
  * @match: Structure containing field and option to probe.

src/lib/fw_config.c

@@ -59,6 +59,21 @@ uint64_t fw_config_get(void)
 	return fw_config_value;
 }
 
+uint64_t fw_config_get_field(const struct fw_config_field *field)
+{
+	/* If fw_config is not provisioned, then there is nothing to get. */
+	if (!fw_config_is_provisioned())
+		return UNDEFINED_FW_CONFIG;
+
+	int shift = __ffs64(field->mask);
+	const uint64_t value = (fw_config_get() & field->mask) >> shift;
+
+	printk(BIOS_INFO, "fw_config get field name=%s, mask=0x%" PRIx64 ", shift=%d, value=0x%"
+		PRIx64 "\n", field->field_name, field->mask, shift, value);
+
+	return value;
+}
+
 bool fw_config_probe(const struct fw_config *match)
 {
 	/* If fw_config is not provisioned, then there is nothing to match. */