boot menu: turn the touchpad driver off, and trace its steps

The ASUS TUF A15 freezes at the default resolution shortly after the
loader hands over -- screen dark, Caps Lock dead -- and it is the only
machine here with an I2C-HID touchpad, which the driver added in the same
release now probes at boot. "Touchpad driver: on/off" in the F8 menu
answers whether it is the cause on the machine itself, through a new
SCHBOOT_OFF_FLAGS byte the kernel checks before starting the driver.

A verbose boot now prints each step of the probe before taking it, so if it
is the cause, the last line on the screen says which step.

Also: S in the menu wrapped at five entries whatever the count.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

boot/uefi/main.c

@@ -118,6 +118,9 @@ static int VERBOSE_BOOT;
 // this particular moment.
 static int DEBUG_BOOT;
 
+// SCHBOOT_OFF_FLAGS: drivers turned off at the boot menu.
+static int OFF_FLAGS;
+
 static void
 serial_putc(char c)
 {
@@ -1539,31 +1542,31 @@ boot_menu(EFI_GRAPHICS_OUTPUT_PROTOCOL *gop)
         // how to make it not refuse. An ISO built for anybody else has no way
         // to turn a network debugger on, because the code that would set the
         // flag is not in it.
-        const char *items[6];
+        const char *items[7];
-        int nitems = 5;
+        int nitems = 6;
         items[0] = "Boot SchOS";
         items[1] = "Boot SchOS (verbose)";
         items[2] = resbuf;
-        items[3] = "System Information";
+        items[3] = (OFF_FLAGS & SCHBOOT_OFF_I2C_HID) ? "Touchpad driver: off"
-        items[4] = "Reboot to firmware";
+                                                     : "Touchpad driver: on";
+        items[4] = "System Information";
+        items[5] = "Reboot to firmware";
 #ifdef SCHOS_DEBUG
-        items[5] = DEBUG_BOOT ? "Remote debugging: on  (schdbgd, port 4444)"
+        items[6] = DEBUG_BOOT ? "Remote debugging: on  (schdbgd, port 4444)"
                               : "Remote debugging: off";
-        nitems = 6;
+        nitems = 7;
 #endif
+        const char *hint = nitems == 7 ? "W/S or 1-7 to choose, Enter to select"
+                                       : "W/S or 1-6 to choose, Enter to select";
 
-        ui_menu("Boot Manager", items, nitems, selected,
+        ui_menu("Boot Manager", items, nitems, selected, hint);
-                nitems == 6 ? "W/S or 1-6 to choose, Enter to select"
-                            : "W/S or 1-5 to choose, Enter to select");
 
         // The same menu on the serial line: the whole thing once, then one
         // line per *move*. Reprinting on every keypress would be correct and
         // unreadable -- a serial terminal has no cursor to paint over, so an
         // unrecognised key would scroll the selection past again for nothing.
         if (echoed < 0) {
-            serial_menu("Boot Manager", items, nitems, selected,
+            serial_menu("Boot Manager", items, nitems, selected, hint, 1);
-                        nitems == 6 ? "W/S or 1-6 to choose, Enter to select"
-                                    : "W/S or 1-5 to choose, Enter to select", 1);
         } else if (echoed != selected) {
             serial_item(items, selected, selected, 1);
         }
@@ -1584,21 +1587,22 @@ boot_menu(EFI_GRAPHICS_OUTPUT_PROTOCOL *gop)
         if (scan == 0x01) { selected = (selected + nitems - 1) % nitems; continue; }
         if (scan == 0x02) { selected = (selected + 1) % nitems; continue; }
         if (c == L'w' || c == L'W') { selected = (selected + nitems - 1) % nitems; continue; }
-        if (c == L's' || c == L'S') { selected = (selected + 1) % 5; continue; }
+        if (c == L's' || c == L'S') { selected = (selected + 1) % nitems; continue; }
         if (c >= L'1' && c <= L'0' + nitems) { selected = (int)(c - L'1'); continue; }
 
         if (c == L'\r' || c == L'\n') {
             if (selected == 0) return 0;
             if (selected == 1) return 1;
             if (selected == 2) { res_choose(gop); continue; }
-            if (selected == 3) { sys_info(gop); continue; }
+            if (selected == 3) { OFF_FLAGS ^= SCHBOOT_OFF_I2C_HID; echoed = -1; continue; }
+            if (selected == 4) { sys_info(gop); continue; }
 #ifdef SCHOS_DEBUG
             // A toggle rather than an action: picking it changes what the
             // entry says and leaves you in the menu, so the state you booted
             // with is the state you can see before you boot.
-            if (selected == 5) { DEBUG_BOOT = !DEBUG_BOOT; echoed = -1; continue; }
+            if (selected == 6) { DEBUG_BOOT = !DEBUG_BOOT; echoed = -1; continue; }
 #endif
-            if (selected == 4) {
+            if (selected == 5) {
                 ui_clear();
                 ui_text_centered((int)ui_height() / 2, "Halted -- reset to reach firmware setup",
                                  0xB9BEC7u);
@@ -2338,6 +2342,7 @@ EfiMain(EFI_HANDLE image, EFI_SYSTEM_TABLE *systab)
     *(UINT32 *)SCHBOOT_EFI_FLAG = SCHBOOT_EFI_MAGIC;
     *(UINT8  *)SCHBOOT_VERBOSE_FLAG = (UINT8)VERBOSE_BOOT;
     *(UINT8  *)SCHBOOT_DEBUG_FLAG   = (UINT8)DEBUG_BOOT;
+    *(UINT8  *)SCHBOOT_OFF_FLAGS    = (UINT8)OFF_FLAGS;
 
     // The page tables mboot_entry would have built. entry64low's first act is
     // a movabs to 0xffff8000...., so the high half must be mapped before the

include/arch/schboot.h

@@ -78,6 +78,13 @@
 // Zero on every ordinary boot, including every boot of a build made without
 // DEBUG=1 -- where the menu entry does not exist and nothing can set it.
 #define SCHBOOT_DEBUG_FLAG    (SCHBOOT_BASE + 0x102)
+
+// Drivers switched off at the boot menu, one bit each. For bisecting a machine
+// that hangs during boot without a rebuild: the newest driver that touches
+// hardware nobody tested it on is the first suspect, and turning it off from
+// the menu answers the question on the machine itself.
+#define SCHBOOT_OFF_FLAGS     (SCHBOOT_BASE + 0x103)
+#define SCHBOOT_OFF_I2C_HID   0x01      // kernel/acpi/i2c_hid.c: touchpads
 #define SCHBOOT_MEDIA_CD      1
 
 // Real-mode spelling of the same byte, for cdboot.S which has no 32-bit

kernel/acpi/i2c_hid.c

@@ -43,6 +43,8 @@
 #include "core/param.h"
 #include "core/spinlock.h"
 #include "arch/mmu.h"
+#include "arch/memlayout.h"
+#include "arch/schboot.h"
 #include "dev/hid.h"
 #include "dev/acpi.h"
 
@@ -51,6 +53,10 @@
 #include <uacpi/namespace.h>
 #include <uacpi/resources.h>
 
+// Each step said before it is taken, in a verbose boot: a machine that stops
+// here stops with the step it was on as the last line on the screen.
+#define STEP(...) do { if(boot_verbose) cprintf(__VA_ARGS__); } while(0)
+
 // ---------------------------------------------------------------------------
 // DesignWare I2C
 // ---------------------------------------------------------------------------
@@ -171,6 +177,7 @@ dw_init(struct dwi2c *c, uacpi_namespace_node *node, uint32 speed)
   c->regs = ioremap(c->phys, 0x1000);
   if(c->regs == 0)
     return -1;
+  STEP("i2c: controller registers at 0x%lx\n", c->phys);
   type = rd(c, IC_COMP_TYPE);
   if(type != DW_COMP_TYPE){
     cprintf("i2c: controller at 0x%lx is not DesignWare (0x%x)\n",
@@ -533,19 +540,24 @@ probe(void *user, uacpi_namespace_node *node, uacpi_u32 depth)
   memset(d, 0, sizeof(*d));
   memmove(d->name, uacpi_namespace_node_name(node).text, 4);
 
+  STEP("i2c-hid: %s: reading its resources\n", d->name);
   if(resources(node, &f) < 0 || !f.i2c){
     cprintf("i2c-hid: %s has no I2C connection\n", d->name);
     return UACPI_ITERATION_DECISION_CONTINUE;
   }
+  STEP("i2c-hid: %s: _DSM\n", d->name);
   if(hid_desc_register(node, &descreg) < 0){
     cprintf("i2c-hid: %s: _DSM gave no descriptor register\n", d->name);
     return UACPI_ITERATION_DECISION_CONTINUE;
   }
+  STEP("i2c-hid: %s: controller %s, address 0x%x\n", d->name, f.bus, f.addr);
   if((d->c = controller(f.bus, f.speed)) == 0)
     return UACPI_ITERATION_DECISION_CONTINUE;
   d->addr = f.addr;
+  STEP("i2c-hid: %s: _PS0\n", d->name);
   uacpi_execute(node, "_PS0", 0);
 
+  STEP("i2c-hid: %s: HID descriptor at register 0x%x\n", d->name, descreg);
   if(reg_read(d, descreg, desc, sizeof(desc)) < 0 ||
      (desc[0] | desc[1] << 8) != 30){
     cprintf("i2c-hid: %s at 0x%x does not answer\n", d->name, d->addr);
@@ -563,6 +575,8 @@ probe(void *user, uacpi_namespace_node *node, uacpi_u32 depth)
   d->pin = interrupt_pin(&f);
   d->active_low = f.active_low;
 
+  STEP("i2c-hid: %s: power on and reset, pin %s\n", d->name,
+       d->pin ? "watched" : "none");
   command(d, OP_SET_POWER, 0);          // 0 = on
   wait_ticks(2);
   command(d, OP_RESET, 0);
@@ -577,6 +591,7 @@ probe(void *user, uacpi_namespace_node *node, uacpi_u32 depth)
     if(dw_xfer(d->c, d->addr, 0, 0, d->buf, d->maxin) < 0)
       break;
 
+  STEP("i2c-hid: %s: report descriptor, %d bytes\n", d->name, rlen);
   if(reg_read(d, rreg, rdesc, rlen) < 0){
     cprintf("i2c-hid: %s: report descriptor unreadable\n", d->name);
     kfree((char *)rdesc);
@@ -603,7 +618,9 @@ i2c_hid_thread(void)
   static const char *const ids[] = { "PNP0C50", "ACPI0C50", 0 };
   int i, n;
 
+  STEP("i2c-hid: looking for touchpads\n");
   uacpi_find_devices_at(uacpi_namespace_root(), ids, probe, 0);
+  STEP("i2c-hid: %d found\n", ndev);
   if(ndev == 0)
     for(;;)
       wait_ticks(1000000);
@@ -630,6 +647,10 @@ i2c_hid_start(void)
 {
   if(acpi_rsdp_phys() == 0)
     return;
+  if(*(volatile uchar *)P2V(SCHBOOT_OFF_FLAGS) & SCHBOOT_OFF_I2C_HID){
+    cprintf("i2c-hid: off, as chosen at the boot menu\n");
+    return;
+  }
   if(kthread_create(i2c_hid_thread, "i2chid") < 0)
     cprintf("i2c-hid: no thread; touchpads will not work\n");
 }