Re: Enabling KGDB for AM335x

[James B <jamesbrowning137%gmail.com@localhost>]

Hi Lloyd,

Thank you for the feedback, I agree that U-Boot is really the correct
place for this. I'll reach out to their community
to see what the best way to handle this is. I suspect they won't want
to change the device tree defaults, but maybe
there's some command  or env variable that can be used to solve this.

I've updated my patch below, I added new params to opt_kgdb.h for
users to specify mux register offsets and values.
I set the defaults to uart1. I also added defaults for the KGDB
rate/mode/address parameters.

Best,
James
=================================================================================
diff -r d708c4dcdd7d sys/arch/arm/ti/files.ti
--- a/sys/arch/arm/ti/files.ti    Sun Apr 27 23:30:39 2025 +0000
+++ b/sys/arch/arm/ti/files.ti    Sun May 25 21:39:29 2025 -0700
@@ -141,4 +141,12 @@
 # SOC parameters
 defflag    opt_soc.h            SOC_TI
 defflag    opt_soc.h            SOC_AM33XX: SOC_TI
-defflag    opt_soc.h            SOC_OMAP3: SOC_TI
+defflag    opt_soc.h           SOC_OMAP3: SOC_TI
+
+# Pins may need to be muxed early to enable kgdb console. This should
be done by
+# the bootloader, but in case it isn't then use this option
+defflag  opt_kgdb.h      TI_EARLY_COM_MUX: SOC_TI,KGDB
+defparam opt_kgdb.h      TI_EARLY_COM_RXOFF=0x980
+                         TI_EARLY_COM_RXVAL=0x30: TI_EARLY_COM_MUX
+defparam opt_kgdb.h      TI_EARLY_COM_TXOFF=0x984
+                         TI_EARLY_COM_TXVAL=0x0: TI_EARLY_COM_MUX
diff -r d708c4dcdd7d sys/arch/arm/ti/ti_com.c
--- a/sys/arch/arm/ti/ti_com.c    Sun Apr 27 23:30:39 2025 +0000
+++ b/sys/arch/arm/ti/ti_com.c    Sun May 25 21:39:29 2025 -0700
@@ -30,6 +30,10 @@

 __KERNEL_RCSID(1, "$NetBSD: ti_com.c,v 1.12 2023/09/05 02:59:07
gutteridge Exp $");

+#ifdef _KERNEL_OPT
+#include "opt_kgdb.h"
+#endif
+
 #include <sys/param.h>
 #include <sys/bus.h>
 #include <sys/device.h>
@@ -44,6 +48,25 @@

 #include <arch/arm/ti/ti_prcm.h>

+#ifdef KGDB
+extern struct bus_space armv7_generic_bs_tag;
+#ifndef KGDB_DEVMODE
+const int comkgdbmode = HUPCL | CS8 | CREAD;
+#else
+const int comkgdbmode = KGDB_DEVMODE;
+#endif
+#ifndef KGDB_DEVADDR
+const int comkgdbaddr = 0x48022000;
+#else
+const int comkgdbaddr = KGDB_DEVADDR;
+#endif
+#ifndef KGDB_DEVRATE
+const int comkgdbrate = 115200;
+#else
+const int comkgdbrate = KGDB_DEVRATE;
+#endif
+#endif
+
 static int ti_com_match(device_t, cfdata_t, void *);
 static void ti_com_attach(device_t, device_t, void *);

@@ -159,6 +182,21 @@

     if (comcnattach1(&regs, speed, uart_freq, COM_TYPE_NORMAL, flags))
         panic("Cannot initialize ti com console");
+
+#if defined(KGDB)
+#if defined(TI_EARLY_COM_MUX)
+    const bus_addr_t ctrl_mod = 0x44E10000;
+    const bus_space_tag_t arm_bst = &armv7_generic_bs_tag;
+    bus_space_handle_t ctrl_bsh;
+
+    bus_space_map(arm_bst, ctrl_mod, 0x2000, 0, &ctrl_bsh);
+    bus_space_write_4(arm_bst, ctrl_bsh, TI_EARLY_COM_RXOFF,
TI_EARLY_COM_RXVAL);
+    bus_space_write_4(arm_bst, ctrl_bsh, TI_EARLY_COM_TXOFF,
TI_EARLY_COM_TXVAL);
+#endif
+    com_init_regs_stride(&regs, bst, dummy_bsh, comkgdbaddr, 2);
+    if (com_kgdb_attach1(&regs, comkgdbrate, uart_freq,
COM_TYPE_OMAP, comkgdbmode))
+      panic("Cannot initialize kgdb console");
+#endif
 }

 static const struct fdt_console ti_com_console = {

On Fri, May 16, 2025 at 1:13 PM Lloyd Parkes
<lloyd%must-have-coffee.gen.nz@localhost> wrote:
>
> Kia ora James,
> I'm no port-arm gatekeeper so I'm not going to answer any of your
> questions about what is right, but I will point out one bit of
> information.
>
> You state in a comment "Need to mux the pins since fdt bus isn't up
> yet". This is only sort-of true.
>
> The NetBSD FDT bus is not ready yet for sure, but U-Boot has already
> initialised the MUX using it's own FDT. You could add uart1
> configuration to the devicetree used by U-Boot and then U-Boot will
> configure the hardware for you. Configuring the hardware so that the
> kernel can boot is one of U-Boot's stated jobs.
>
> The kernel can support both methods with a #ifdef option.
>
> Whether or not you want to put that work into U-Boot is up to you.
>
> Ngā mihi,
> Lloyd
>