[PATCH v2 1/3] serial: goldfish: Add debug uart support

[PATCH v2 1/3] serial: goldfish: Add debug uart support

[Daniel Palmer]

Add debug support for the goldfish tty so it can be used for
early debugging. This will be really useful when adding support
for relocation to the m68k qemu virt machine.

Signed-off-by: Daniel Palmer <daniel@0x0f.com>
---
 drivers/serial/Kconfig           |  8 ++++++++
 drivers/serial/serial_goldfish.c | 18 ++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index b84cb9ec781d..f6a696e6c94c 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -510,6 +510,14 @@ config DEBUG_UART_XTENSA_SEMIHOSTING
 	  start up driver model. The driver will be available until the real
 	  driver model serial is running.
 
+config DEBUG_UART_GOLDFISH
+	bool "Goldfish TTY"
+	help
+	  Select this to enable the debug UART using the Goldfish TTY driver.
+	  This provides basic serial output from the console without needing to
+	  start up driver model. The driver will be available until the real
+	  driver model serial is running.
+
 endchoice
 
 config DEBUG_UART_BASE
diff --git a/drivers/serial/serial_goldfish.c b/drivers/serial/serial_goldfish.c
index 4ac2cfb62315..91dc040fcf26 100644
--- a/drivers/serial/serial_goldfish.c
+++ b/drivers/serial/serial_goldfish.c
@@ -115,3 +115,21 @@ U_BOOT_DRIVER(serial_goldfish) = {
 	.priv_auto = sizeof(struct goldfish_tty_priv),
 	.flags	= DM_FLAG_PRE_RELOC,
 };
+
+#ifdef CONFIG_DEBUG_UART_GOLDFISH
+
+#include <debug_uart.h>
+
+static inline void _debug_uart_init(void)
+{
+}
+
+static inline void _debug_uart_putc(int ch)
+{
+	void __iomem *base = (void __iomem *)CONFIG_VAL(DEBUG_UART_BASE);
+
+	__raw_writel(ch, base + GOLDFISH_TTY_PUT_CHAR);
+}
+
+DEBUG_UART_FUNCS
+#endif
-- 
2.51.0

[PATCH v2 2/3] m68k: m680x0: Initialise the debug uart

[Daniel Palmer]

Once the stack is ready we can init the debug uart to help
with debugging so do that.

Signed-off-by: Daniel Palmer <daniel@0x0f.com>
---
 arch/m68k/cpu/m680x0/start.S | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/m68k/cpu/m680x0/start.S b/arch/m68k/cpu/m680x0/start.S
index 0802ca1fca2c..fdfcd66f7785 100644
--- a/arch/m68k/cpu/m680x0/start.S
+++ b/arch/m68k/cpu/m680x0/start.S
@@ -42,6 +42,11 @@ ENTRY(_start)
 	/* Setup initial stack pointer */
 	move.l	#CFG_SYS_INIT_SP_ADDR, %sp
 
+	/* Setup the debug uart if enabled */
+#ifdef CONFIG_DEBUG_UART
+	bsr.l	debug_uart_init
+#endif
+
 	/*
 	 * Allocate Global Data (GD)
 	 * board_init_f_alloc_reserve(top) returns the new top of stack in %d0
-- 
2.51.0

[PATCH v2 3/3] doc: board: virt: m68k: Detail how to use debug uart

[Daniel Palmer]

Add a paragraph to explain how to get the address of the goldfish
tty and use it as the debug uart. I think the address is actually
fixed right now but it might change in the future.

Signed-off-by: Daniel Palmer <daniel@0x0f.com>
---
 doc/board/emulation/qemu-m68k.rst | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/doc/board/emulation/qemu-m68k.rst b/doc/board/emulation/qemu-m68k.rst
index 6c4de54cf6a8..2f2e6bd6444a 100644
--- a/doc/board/emulation/qemu-m68k.rst
+++ b/doc/board/emulation/qemu-m68k.rst
@@ -31,6 +31,16 @@ The minimal QEMU command line to get U-Boot up and running is:
 Note that the `-nographic` option is used to redirect the console to stdio,
 which connects to the emulated Goldfish TTY device.
 
+Debugging U-Boot
+----------------
+
+If you need early debugging output enable `CONFIG_DEBUG_UART_GOLDFISH`.
+The base address for the UART can be found by activating the QEMU monitor,
+running `info qtree`, and then looking for the goldfish tty device and
+taking the mmio address.
+
+Baud rate doesn't matter.
+
 Hardware Support
 ----------------
 The following QEMU virt peripherals are supported in U-Boot:
-- 
2.51.0

Re: [PATCH v2 2/3] m68k: m680x0: Initialise the debug uart

[Kuan-Wei Chiu]

+Cc Angelo since this touches arch/m68k/

On Mon, Mar 09, 2026 at 07:51:09PM +0900, Daniel Palmer wrote:
> Once the stack is ready we can init the debug uart to help
> with debugging so do that.
> 
> Signed-off-by: Daniel Palmer <daniel@0x0f.com>
> ---
>  arch/m68k/cpu/m680x0/start.S | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/m68k/cpu/m680x0/start.S b/arch/m68k/cpu/m680x0/start.S
> index 0802ca1fca2c..fdfcd66f7785 100644
> --- a/arch/m68k/cpu/m680x0/start.S
> +++ b/arch/m68k/cpu/m680x0/start.S
> @@ -42,6 +42,11 @@ ENTRY(_start)
>  	/* Setup initial stack pointer */
>  	move.l	#CFG_SYS_INIT_SP_ADDR, %sp
>  
> +	/* Setup the debug uart if enabled */
> +#ifdef CONFIG_DEBUG_UART
> +	bsr.l	debug_uart_init
> +#endif
> +
>  	/*
>  	 * Allocate Global Data (GD)
>  	 * board_init_f_alloc_reserve(top) returns the new top of stack in %d0
> -- 
> 2.51.0
> 

Re: [PATCH v2 1/3] serial: goldfish: Add debug uart support

[Kuan-Wei Chiu]

On Mon, Mar 09, 2026 at 07:51:08PM +0900, Daniel Palmer wrote:
> Add debug support for the goldfish tty so it can be used for
> early debugging. This will be really useful when adding support
> for relocation to the m68k qemu virt machine.
> 
> Signed-off-by: Daniel Palmer <daniel@0x0f.com>
> ---
>  drivers/serial/Kconfig           |  8 ++++++++
>  drivers/serial/serial_goldfish.c | 18 ++++++++++++++++++
>  2 files changed, 26 insertions(+)

For the series:

Reviewed-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Tested-by: Kuan-Wei Chiu <visitorckw@gmail.com>

Hi Tom,
Would you take this patchset directly, or would you prefer a pull
request?

Regards,
Kuan-Wei

Re: [PATCH v2 2/3] m68k: m680x0: Initialise the debug uart

[Angelo Dureghello]

Acked-by: Angelo Dureghello <angelo@kernel-space.org>

On 3/10/26 06:58, Kuan-Wei Chiu wrote:
> +Cc Angelo since this touches arch/m68k/
> 
> On Mon, Mar 09, 2026 at 07:51:09PM +0900, Daniel Palmer wrote:
>> Once the stack is ready we can init the debug uart to help
>> with debugging so do that.
>>
>> Signed-off-by: Daniel Palmer <daniel@0x0f.com>
>> ---
>>  arch/m68k/cpu/m680x0/start.S | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/arch/m68k/cpu/m680x0/start.S b/arch/m68k/cpu/m680x0/start.S
>> index 0802ca1fca2c..fdfcd66f7785 100644
>> --- a/arch/m68k/cpu/m680x0/start.S
>> +++ b/arch/m68k/cpu/m680x0/start.S
>> @@ -42,6 +42,11 @@ ENTRY(_start)
>>  	/* Setup initial stack pointer */
>>  	move.l	#CFG_SYS_INIT_SP_ADDR, %sp
>>  
>> +	/* Setup the debug uart if enabled */
>> +#ifdef CONFIG_DEBUG_UART
>> +	bsr.l	debug_uart_init
>> +#endif
>> +
>>  	/*
>>  	 * Allocate Global Data (GD)
>>  	 * board_init_f_alloc_reserve(top) returns the new top of stack in %d0
>> -- 
>> 2.51.0
>>

-- Angelo

Re: [PATCH v2 1/3] serial: goldfish: Add debug uart support

[Tom Rini]

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On Tue, Mar 10, 2026 at 02:07:53PM +0800, Kuan-Wei Chiu wrote:
> On Mon, Mar 09, 2026 at 07:51:08PM +0900, Daniel Palmer wrote:
> > Add debug support for the goldfish tty so it can be used for
> > early debugging. This will be really useful when adding support
> > for relocation to the m68k qemu virt machine.
> > 
> > Signed-off-by: Daniel Palmer <daniel@0x0f.com>
> > ---
> >  drivers/serial/Kconfig           |  8 ++++++++
> >  drivers/serial/serial_goldfish.c | 18 ++++++++++++++++++
> >  2 files changed, 26 insertions(+)
> 
> For the series:
> 
> Reviewed-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> Tested-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> 
> Hi Tom,
> Would you take this patchset directly, or would you prefer a pull
> request?

I will apply this to next directly, after it's been posted for about 2
weeks to allow for other reviews.

-- 
Tom

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Re: [PATCH v2 1/3] serial: goldfish: Add debug uart support

[Kuan-Wei Chiu]

On Tue, Mar 10, 2026 at 10:25:34AM -0600, Tom Rini wrote:
> On Tue, Mar 10, 2026 at 02:07:53PM +0800, Kuan-Wei Chiu wrote:
> > On Mon, Mar 09, 2026 at 07:51:08PM +0900, Daniel Palmer wrote:
> > > Add debug support for the goldfish tty so it can be used for
> > > early debugging. This will be really useful when adding support
> > > for relocation to the m68k qemu virt machine.
> > > 
> > > Signed-off-by: Daniel Palmer <daniel@0x0f.com>
> > > ---
> > >  drivers/serial/Kconfig           |  8 ++++++++
> > >  drivers/serial/serial_goldfish.c | 18 ++++++++++++++++++
> > >  2 files changed, 26 insertions(+)
> > 
> > For the series:
> > 
> > Reviewed-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> > Tested-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> > 
> > Hi Tom,
> > Would you take this patchset directly, or would you prefer a pull
> > request?
> 
> I will apply this to next directly, after it's been posted for about 2
> weeks to allow for other reviews.

Sure. Thanks!
I just wanted to clarify who would be picking it up after the review
period, so it doesn't fall through the cracks.

Regards,
Kuan-Wei