fw_config: Add firmware configuration interface

This change introduces a new top-level interface for interacting with a
bitmask providing firmware configuration information.

This is motivated by Chromebook mainboards that need to support multiple
different configurations at runtime with the same BIOS.  In these
devices the Embedded Controller provides a bitmask that can be broken
down into different fields and each field can then be broken down into
different options.

The firmware configuration value could also be stored in CBFS and this
interface will look in CBFS first to allow the Embedded Controller value
to be overridden.

The firmware configuration interface is intended to easily integrate
into devicetree.cb and lead to less code duplication for new mainboards
that make use of this feature.

BUG=b:147462631
TEST=this provides a new interface that is tested in subsequent commits

Change-Id: I1e889c235a81545e2ec0e3a34dfa750ac828a330
Signed-off-by: Duncan Laurie <dlaurie@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41209
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/lib/Makefile.inc

@@ -159,6 +159,11 @@ romstage-y += hexdump.c
 verstage-y += hexdump.c
 smm-y += hexdump.c
 
+bootblock-$(CONFIG_FW_CONFIG) += fw_config.c
+verstage-$(CONFIG_FW_CONFIG) += fw_config.c
+romstage-$(CONFIG_FW_CONFIG) += fw_config.c
+ramstage-$(CONFIG_FW_CONFIG) += fw_config.c
+
 bootblock-$(CONFIG_ESPI_DEBUG) += espi_debug.c
 verstage-$(CONFIG_ESPI_DEBUG) += espi_debug.c
 romstage-$(CONFIG_ESPI_DEBUG) += espi_debug.c

src/lib/fw_config.c

@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <bootstate.h>
+#include <cbfs.h>
+#include <console/console.h>
+#include <device/device.h>
+#include <ec/google/chromeec/ec.h>
+#include <fw_config.h>
+#include <stdbool.h>
+#include <stdint.h>
+
+/**
+ * fw_config_get() - Provide firmware configuration value.
+ *
+ * Return 32bit firmware configuration value determined for the system.
+ */
+static uint32_t fw_config_get(void)
+{
+	static uint32_t fw_config_value;
+	static bool fw_config_value_initialized;
+
+	/* Nothing to prepare if setup is already done. */
+	if (fw_config_value_initialized)
+		return fw_config_value;
+	fw_config_value_initialized = true;
+
+	/* Look in CBFS to allow override of value. */
+	if (CONFIG(FW_CONFIG_SOURCE_CBFS)) {
+		if (cbfs_boot_load_file(CONFIG_CBFS_PREFIX "/fw_config",
+					&fw_config_value, sizeof(fw_config_value),
+					CBFS_TYPE_RAW) != sizeof(fw_config_value)) {
+			printk(BIOS_WARNING, "%s: Could not get fw_config from CBFS\n",
+			       __func__);
+			fw_config_value = 0;
+		} else {
+			printk(BIOS_INFO, "FW_CONFIG value from CBFS is 0x%08x\n",
+			       fw_config_value);
+			return fw_config_value;
+		}
+	}
+
+	/* Read the value from EC CBI. */
+	if (CONFIG(FW_CONFIG_SOURCE_CHROMEEC_CBI)) {
+		if (google_chromeec_cbi_get_fw_config(&fw_config_value))
+			printk(BIOS_WARNING, "%s: Could not get fw_config from EC\n", __func__);
+	}
+
+	printk(BIOS_INFO, "FW_CONFIG value is 0x%08x\n", fw_config_value);
+	return fw_config_value;
+}
+
+bool fw_config_probe(const struct fw_config *match)
+{
+	/* Compare to system value. */
+	if ((fw_config_get() & match->mask) == match->value) {
+		if (match->field_name && match->option_name)
+			printk(BIOS_INFO, "fw_config match found: %s=%s\n", match->field_name,
+			       match->option_name);
+		else
+			printk(BIOS_INFO, "fw_config match found: mask=0x%08x value=0x%08x\n",
+			       match->mask, match->value);
+		return true;
+	}
+
+	return false;
+}
+
+#if ENV_RAMSTAGE
+static void fw_config_init(void *unused)
+{
+	struct device *dev;
+
+	for (dev = all_devices; dev; dev = dev->next) {
+		const struct fw_config *probe;
+		bool match = false;
+
+		if (!dev->probe_list)
+			continue;
+
+		for (probe = dev->probe_list; probe && probe->mask != 0; probe++) {
+			if (fw_config_probe(probe)) {
+				match = true;
+				break;
+			}
+		}
+
+		if (!match) {
+			printk(BIOS_INFO, "%s disabled by fw_config\n", dev_path(dev));
+			dev->enabled = 0;
+		}
+	}
+}
+BOOT_STATE_INIT_ENTRY(BS_DEV_ENUMERATE, BS_ON_ENTRY, fw_config_init, NULL);
+#endif