From 055f03980c567a594c7fc0cb94264cc30a579519 Mon Sep 17 00:00:00 2001
From: Rodrigo Arias Mallo <rodarima@gmail.com>
Date: Fri, 2 Aug 2024 13:18:18 +0200
Subject: [PATCH] Add exception sregs command to U-Boot

---
 JOURNAL.md        | 31 +++++++++++++++++++++++++++++--
 lagarto-ox.nix    |  2 ++
 uboot-sregs.patch | 45 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 76 insertions(+), 2 deletions(-)
 create mode 100644 uboot-sregs.patch

diff --git a/JOURNAL.md b/JOURNAL.md
index 88b4d27..23e2cb1 100644
--- a/JOURNAL.md
+++ b/JOURNAL.md
@@ -3300,10 +3300,15 @@ mode interrupts unconditionally.
 
 Let's try to cause an interruption. I would need to list all the steps.
 
+    mw 0x40014000 0xffffffff # Disable clock interrupt
+    md 0x40801000 1 # Show pending interrupts (should be 0x10)
     mw 0x40802000 0x10 # Enable interrupt for source 4 (timer)
     mw 0x40800010 0xff # Make source 4 priority large
-    md 0x40a00004 1 # Show which value should be claimed
-    mw 0x40a00004 0 # Claim 0
+    md 0x40a00004 1 # Claim interrupt (should read 4)
+    mw 0x40a00004 4 # Complete 4
+    md 0x40801000 1 # Show pending interrupts (should be 0x00)
+    mw 0x40014000 0x00000000 # Enable clock interrupt (should cause one)
+    md 0x40801000 1 # Show pending interrupts (should be 0x10)
 
 Nice, I can see the trap:
 
@@ -3338,3 +3343,25 @@ Nice, I can see the trap:
     sbi_trap_error: hart0: trap0: t6=0x00000000aeed3aa0
 
 Now let's try delegating it to u-boot, and see if I can print some information.
+
+I don't see any message:
+
+    Boot HART MIDELEG         : 0x0000000000000222
+    Boot HART MEDELEG         : 0x000000000000b109
+    ...
+    => mw 0x40014000 0xffffffff # Disable clock interrupt
+    => md 0x40801000 1 # Show pending interrupts (should be 0x10)
+    40801000: 00000010                             ....
+    => mw 0x40802000 0x10 # Enable interrupt for source 4 (timer)
+    => mw 0x40800010 0xff # Make source 4 priority large
+    => md 0x40a00004 1 # Claim interrupt (should read 4)
+    40a00004: 00000004                             ....
+    => mw 0x40a00004 4 # Complete 4
+    => md 0x40801000 1 # Show pending interrupts (should be 0x00)
+    40801000: 00000000                             ....
+    => mw 0x40014000 0x00000000 # Enable clock interrupt (should cause one)
+    => md 0x40801000 1 # Show pending interrupts (should be 0x10)
+    40801000: 00000010
+
+I made a small subcommand U-Boot "exception sregs" to be able to dump the
+supervisor registers, to check they have the proper values.
diff --git a/lagarto-ox.nix b/lagarto-ox.nix
index dcdb300..fabab92 100644
--- a/lagarto-ox.nix
+++ b/lagarto-ox.nix
@@ -219,6 +219,7 @@
       patches = [
         #./u-boot-debug.patch
         ./uboot-debug-ext-interrupts.patch
+        ./uboot-sregs.patch
       ];
       #
       # CONFIG_SERIAL_PRESENT=n
@@ -245,6 +246,7 @@
         CONFIG_SMP=n
         CONFIG_TRACE_EARLY=y
         CONFIG_CMD_MEMTEST=y
+        CONFIG_CMD_EXCEPTION=y
       ''
 #      # Enable debug logs
 #      +
diff --git a/uboot-sregs.patch b/uboot-sregs.patch
new file mode 100644
index 0000000..ad707e1
--- /dev/null
+++ b/uboot-sregs.patch
@@ -0,0 +1,45 @@
+diff --git a/cmd/riscv/exception.c b/cmd/riscv/exception.c
+index f38f454a0b..87877ab235 100644
+--- a/cmd/riscv/exception.c
++++ b/cmd/riscv/exception.c
+@@ -56,6 +56,23 @@ static int do_undefined(struct cmd_tbl *cmdtp, int flag, int argc,
+ 	return CMD_RET_FAILURE;
+ }
+ 
++static int do_sregs(struct cmd_tbl *cmdtp, int flag, int argc,
++			char *const argv[])
++{
++	ulong stvec, sie, sstatus;
++
++	asm volatile ("fence");
++	asm volatile ("csrr %0, stvec" : "=r"(stvec) : );
++	asm volatile ("csrr %0, sie" : "=r"(sie) : );
++	asm volatile ("csrr %0, sstatus" : "=r"(sstatus) : );
++
++	printf("stvec   : 0x%08lx\n", stvec);
++	printf("sie     : 0x%08lx\n", sie);
++	printf("sstatus : 0x%08lx\n", sstatus);
++
++	return CMD_RET_SUCCESS;
++}
++
+ static struct cmd_tbl cmd_sub[] = {
+ 	U_BOOT_CMD_MKENT(compressed, CONFIG_SYS_MAXARGS, 1, do_compressed,
+ 			 "", ""),
+@@ -67,6 +84,8 @@ static struct cmd_tbl cmd_sub[] = {
+ 			 "", ""),
+ 	U_BOOT_CMD_MKENT(undefined, CONFIG_SYS_MAXARGS, 1, do_undefined,
+ 			 "", ""),
++	U_BOOT_CMD_MKENT(sregs, CONFIG_SYS_MAXARGS, 1, do_sregs,
++			 "", ""),
+ };
+ 
+ static char exception_help_text[] =
+@@ -77,6 +96,7 @@ static char exception_help_text[] =
+ 	"  ialign16   - 16 bit aligned instruction\n"
+ 	"  undefined  - illegal instruction\n"
+ 	"  unaligned  - load address misaligned\n"
++	"  sregs      - print supervisor registers\n"
+ 	;
+ 
+ #include <exception.h>