From c0fd295cf44dd482996390f9d489787e12003c99 Mon Sep 17 00:00:00 2001
From: mintsuki <mintsuki@protonmail.com>
Date: Thu, 8 Feb 2024 09:30:59 +0100
Subject: [PATCH] serial: Add baudrate setting for BIOS

Co-authored-by: Bryce Lanham <blanham@gmail.com>
---
 CONFIG.md                                |  1 +
 common/drivers/{serial.s2.c => serial.c} | 17 +++++++++++++++--
 common/lib/print.s2.c                    |  2 +-
 common/linker_bios.ld.in                 |  1 +
 4 files changed, 18 insertions(+), 3 deletions(-)
 rename common/drivers/{serial.s2.c => serial.c} (62%)

diff --git a/CONFIG.md b/CONFIG.md
index 0652673c..85675598 100644
--- a/CONFIG.md
+++ b/CONFIG.md
@@ -59,6 +59,7 @@ Miscellaneous:
 * `TIMEOUT` - Specifies the timeout in seconds before the first *entry* is automatically booted. If set to `no`, disable automatic boot. If set to `0`, boots default entry instantly (see `DEFAULT_ENTRY` key).
 * `QUIET` - If set to `yes`, enable quiet mode, where all screen output except panics and important warnings is suppressed. If `TIMEOUT` is not 0, the `TIMEOUT` still occurs, and pressing any key during the timeout will reveal the menu and disable quiet mode.
 * `SERIAL` - If set to `yes`, enable serial I/O for the bootloader.
+* `SERIAL_BAUDRATE` - If `SERIAL` is set to `yes`, this specifies the baudrate to use for serial I/O. Defaults to `9600`. BIOS only, ignored with Limine UEFI.
 * `DEFAULT_ENTRY` - 1-based entry index of the entry which will be automatically selected at startup. If unspecified, it is `1`.
 * `GRAPHICS` - If set to `no`, force CGA text mode for the boot menu, else use a video mode. Ignored with Limine UEFI.
 * `VERBOSE` - If set to `yes`, print additional information during boot. Defaults to not verbose.
diff --git a/common/drivers/serial.s2.c b/common/drivers/serial.c
similarity index 62%
rename from common/drivers/serial.s2.c
rename to common/drivers/serial.c
index f2c885f3..4038caf9 100644
--- a/common/drivers/serial.s2.c
+++ b/common/drivers/serial.c
@@ -6,19 +6,32 @@
 #include <drivers/serial.h>
 #include <sys/cpu.h>
 #include <lib/misc.h>
+#include <lib/config.h>
 
 static bool serial_initialised = false;
+static uint32_t serial_baudrate;
 
 static void serial_initialise(void) {
-    if (serial_initialised) {
+    if (serial_initialised || config_ready == false) {
         return;
     }
 
+    char *baudrate_s = config_get_value(NULL, 0, "SERIAL_BAUDRATE");
+    if (baudrate_s == NULL) {
+        serial_baudrate = 9600;
+    } else {
+        serial_baudrate = strtoui(baudrate_s, NULL, 10);
+    }
+
     // Init com1
     outb(0x3f8 + 3, 0x00);
     outb(0x3f8 + 1, 0x00);
     outb(0x3f8 + 3, 0x80);
-    outb(0x3f8 + 0, 0x0c); // 9600 baud
+
+    uint16_t divisor = (uint16_t)(115200 / serial_baudrate);
+    outb(0x3f8 + 0, divisor & 0xff);
+    outb(0x3f8 + 1, (divisor >> 8) & 0xff);
+
     outb(0x3f8 + 1, 0x00);
     outb(0x3f8 + 3, 0x03);
     outb(0x3f8 + 2, 0xc7);
diff --git a/common/lib/print.s2.c b/common/lib/print.s2.c
index 45a4779f..d382c358 100644
--- a/common/lib/print.s2.c
+++ b/common/lib/print.s2.c
@@ -237,7 +237,7 @@ out:
         }
 #endif
 #if defined (BIOS)
-        if ((!quiet && serial) || COM_OUTPUT) {
+        if (stage3_loaded && ((!quiet && serial) || COM_OUTPUT)) {
             switch (print_buf[i]) {
                 case '\n':
                     serial_out('\r');
diff --git a/common/linker_bios.ld.in b/common/linker_bios.ld.in
index 7a7d024f..095b075e 100644
--- a/common/linker_bios.ld.in
+++ b/common/linker_bios.ld.in
@@ -42,6 +42,7 @@ SECTIONS
         term_notready = .;
         terms = .;
         terms_i = .;
+        serial_out = .;
         stage3_addr = .;
 #else
 #ifdef LINKER_NOS2MAP