drivers/ocp/vpd: Overwrite Linux payload's kernel command via VPD

Add a new Kconfig LINUXPAYLOAD_CMDLINE_VPD_OVERWRITE that can overwrite
Linux payload's kernel command line from VPD. Currently only overwrite
Linux kernel command line 'loglevel' via VPD key 'kernel_log_level'.

TESTED=On OCP Delta Lake, with kernel_log_level set to 0, warm reboot
time can see about 10 seconds improvement comparing to kernel log level
7.

Change-Id: Idf06c7ab9958c940fc3b23d560bb9dade991a6da
Signed-off-by: Johnny Lin <johnny_lin@wiwynn.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/75510
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>

src/drivers/ocp/include/vpd.h

@@ -77,6 +77,9 @@ enum cxl_memory_mode {
 /* Socket 1 core disable bitmask */
 #define CORE_DIS_BITMSK1 "core_disable_bitmask1"
 
+/* Linux payload kernel log level */
+#define KERNEL_LOG_LEVEL "kernel_log_level"
+
 /* Get VPD key with provided fallback value and min/max ranges */
 int get_int_from_vpd_range(const char *const key, const int fallback, const int min,
 	const int max);

src/drivers/ocp/vpd/Kconfig

@@ -4,3 +4,12 @@ config OCP_VPD
 	depends on VPD
 	help
 	  It implements functions that get common VPD variables for OCP projects.
+
+config LINUXPAYLOAD_CMDLINE_VPD_OVERWRITE
+	bool
+	default n
+	depends on VPD
+	help
+	  Overwrite Linux payload's kernel command line by using VPD. Currently only
+	  overwrite the value of kernel command line 'loglevel'. The Linux kernel command
+	  line data is detected in the last segment loaded in memory and overwritten.

src/drivers/ocp/vpd/Makefile.inc

@@ -1,5 +1,6 @@
 romstage-$(CONFIG_OCP_VPD) += vpd_util.c
 ramstage-$(CONFIG_OCP_VPD) += vpd_util.c
+ramstage-$(CONFIG_LINUXPAYLOAD_CMDLINE_VPD_OVERWRITE) += vpd_cmdline.c
 ifeq ($(CONFIG_VPD),y)
 all-$(CONFIG_CONSOLE_OVERRIDE_LOGLEVEL) += loglevel_vpd.c
 endif

src/drivers/ocp/vpd/vpd_cmdline.c

@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <console/console.h>
+#include <drivers/vpd/vpd.h>
+#include <drivers/ocp/include/vpd.h>
+#include <string.h>
+#include <program_loading.h>
+
+#define CMDLINE_LOGLVL_STR	"loglevel="
+
+static void overwrite_kernel_loglevel(uintptr_t start)
+{
+	int val;
+	if (!vpd_get_int(KERNEL_LOG_LEVEL, VPD_RW_THEN_RO, &val)) {
+		printk(BIOS_DEBUG, "%s: not able to get VPD %s\n", __func__, KERNEL_LOG_LEVEL);
+		return;
+	}
+
+	printk(BIOS_DEBUG, "%s: VPD %s, got %d\n", __func__, KERNEL_LOG_LEVEL, val);
+	if (val < 0 || val > 7) {
+		printk(BIOS_INFO, "Invalid VPD for Linux kernel log level\n");
+		return;
+	}
+
+	int loglevel;
+	char *loc = strstr((const char *)start, CMDLINE_LOGLVL_STR);
+	if (!loc) {
+		printk(BIOS_INFO, "%s is not found from LINUX_COMMAND_LINE\n",
+			CMDLINE_LOGLVL_STR);
+		return;
+	}
+
+	char *loc_bkup;
+	loc += strlen(CMDLINE_LOGLVL_STR);
+	loc_bkup = loc;
+	loglevel = skip_atoi(&loc);
+	printk(BIOS_DEBUG, "Original kernel log level is %d\n", loglevel);
+	/* Unlikely but don't overwrite with such an unexpected case. */
+	if (loglevel < 0 || loglevel > 7) {
+		printk(BIOS_DEBUG, "Invalid kernel log level, must be from 0 to 7.\n");
+		return;
+	}
+
+	char c = '0' + val;
+	printk(BIOS_INFO, "Overwrite kernel log level with %c from VPD.\n", c);
+	memcpy(loc_bkup, &c, 1);
+}
+
+void platform_segment_loaded(uintptr_t start, size_t size, int flags)
+{
+	/* CONFIG_LINUX_COMMAND_LINE is in the final segment. */
+	if (flags != SEG_FINAL)
+		return;
+
+	overwrite_kernel_loglevel(start);
+}