[RFC] powerpc: udbg: export udbg_putc

  In a randconfig with CONFIG_SERIAL_CPM=m and
CONFIG_PPC_EARLY_DEBUG_CPM=y, there is a build error:
ERROR: modpost: "udbg_putc" [drivers/tty/serial/cpm_uart/cpm_uart.ko] undefined!

The build can be fixed by exporting "udbg_putc" in udbg.c.

OTOH, maybe something like this is more appropriate in
arch/powerpc/Kconfig.debug?

config PPC_EARLY_DEBUG_CPM
	bool "Early serial debugging for Freescale CPM-based serial ports"
-	depends on SERIAL_CPM
+	depends on SERIAL_CPM=y

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Pali Rohár" <pali@kernel.org>
---
 arch/powerpc/kernel/udbg.c |    1 +
 1 file changed, 1 insertion(+)
  

On Friday 12 May 2023 22:58:04 Randy Dunlap wrote:
> In a randconfig with CONFIG_SERIAL_CPM=m and
> CONFIG_PPC_EARLY_DEBUG_CPM=y, there is a build error:
> ERROR: modpost: "udbg_putc" [drivers/tty/serial/cpm_uart/cpm_uart.ko] undefined!
> 
> The build can be fixed by exporting "udbg_putc" in udbg.c.
> 
> OTOH, maybe something like this is more appropriate in
> arch/powerpc/Kconfig.debug?
> 
> config PPC_EARLY_DEBUG_CPM
> 	bool "Early serial debugging for Freescale CPM-based serial ports"
> -	depends on SERIAL_CPM
> +	depends on SERIAL_CPM=y
> 
> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: "Pali Rohár" <pali@kernel.org>
> ---
>  arch/powerpc/kernel/udbg.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff -- a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c
> --- a/arch/powerpc/kernel/udbg.c
> +++ b/arch/powerpc/kernel/udbg.c
> @@ -14,6 +14,7 @@
>  #include <asm/udbg.h>
>  
>  void (*udbg_putc)(char c);
> +EXPORT_SYMBOL(udbg_putc);
>  void (*udbg_flush)(void);
>  int (*udbg_getc)(void);
>  int (*udbg_getc_poll)(void);

Hello! I do not think that it is a good idea to export udbg functions
for kernel modules. I have quickly looked at the cpm_uart driver file
drivers/tty/serial/cpm_uart/cpm_uart_core.c and it looks like that once
udbg from it is registered then there is no code for unregistering it.
So I have feeling that compiling cpm_uart driver as module should not be
allowed when CONFIG_SERIAL_CPM_CONSOLE is enabled, and early debug
should depend on CONFIG_CONSOLE_POLL || CONFIG_SERIAL_CPM_CONSOLE.

Any other opinion?
  

Hi Pali,

On 5/13/23 02:13, Pali Rohár wrote:
> On Friday 12 May 2023 22:58:04 Randy Dunlap wrote:
>> In a randconfig with CONFIG_SERIAL_CPM=m and
>> CONFIG_PPC_EARLY_DEBUG_CPM=y, there is a build error:
>> ERROR: modpost: "udbg_putc" [drivers/tty/serial/cpm_uart/cpm_uart.ko] undefined!
>>
>> The build can be fixed by exporting "udbg_putc" in udbg.c.
>>
>> OTOH, maybe something like this is more appropriate in
>> arch/powerpc/Kconfig.debug?
>>
>> config PPC_EARLY_DEBUG_CPM
>> 	bool "Early serial debugging for Freescale CPM-based serial ports"
>> -	depends on SERIAL_CPM
>> +	depends on SERIAL_CPM=y
>>
>> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: Nicholas Piggin <npiggin@gmail.com>
>> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
>> Cc: linuxppc-dev@lists.ozlabs.org
>> Cc: Arnd Bergmann <arnd@arndb.de>
>> Cc: "Pali Rohár" <pali@kernel.org>
>> ---
>>  arch/powerpc/kernel/udbg.c |    1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff -- a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c
>> --- a/arch/powerpc/kernel/udbg.c
>> +++ b/arch/powerpc/kernel/udbg.c
>> @@ -14,6 +14,7 @@
>>  #include <asm/udbg.h>
>>  
>>  void (*udbg_putc)(char c);
>> +EXPORT_SYMBOL(udbg_putc);
>>  void (*udbg_flush)(void);
>>  int (*udbg_getc)(void);
>>  int (*udbg_getc_poll)(void);
> 
> Hello! I do not think that it is a good idea to export udbg functions
> for kernel modules. I have quickly looked at the cpm_uart driver file

Sure, that was just a conversation starter.

> drivers/tty/serial/cpm_uart/cpm_uart_core.c and it looks like that once
> udbg from it is registered then there is no code for unregistering it.
> So I have feeling that compiling cpm_uart driver as module should not be
> allowed when CONFIG_SERIAL_CPM_CONSOLE is enabled, and early debug
> should depend on CONFIG_CONSOLE_POLL || CONFIG_SERIAL_CPM_CONSOLE.

The other change above also fixes the build error: (Option 2)

>> config PPC_EARLY_DEBUG_CPM
>> 	bool "Early serial debugging for Freescale CPM-based serial ports"
>> -	depends on SERIAL_CPM
>> +	depends on SERIAL_CPM=y


Also, making SERIAL_CPM (cpm_uart driver) be restricted to not allow it
as a module when SERIAL_CPM_CONSOLE is enabled [how does one express that
in Kconfig language?] will cause a circular dependency since SERIAL_CPM_CONSOLE
depends on SERIAL_CPM=y. It looks like you are suggesting reversing the
dependencies.

> Any other opinion?

Yes, please. Otherwise I prefer my option 2.
  

On Saturday 13 May 2023 15:53:19 Randy Dunlap wrote:
> Hi Pali,
> 
> On 5/13/23 02:13, Pali Rohár wrote:
> > On Friday 12 May 2023 22:58:04 Randy Dunlap wrote:
> >> In a randconfig with CONFIG_SERIAL_CPM=m and
> >> CONFIG_PPC_EARLY_DEBUG_CPM=y, there is a build error:
> >> ERROR: modpost: "udbg_putc" [drivers/tty/serial/cpm_uart/cpm_uart.ko] undefined!
> >>
> >> The build can be fixed by exporting "udbg_putc" in udbg.c.
> >>
> >> OTOH, maybe something like this is more appropriate in
> >> arch/powerpc/Kconfig.debug?
> >>
> >> config PPC_EARLY_DEBUG_CPM
> >> 	bool "Early serial debugging for Freescale CPM-based serial ports"
> >> -	depends on SERIAL_CPM
> >> +	depends on SERIAL_CPM=y
> >>
> >> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
> >> Cc: Michael Ellerman <mpe@ellerman.id.au>
> >> Cc: Nicholas Piggin <npiggin@gmail.com>
> >> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> >> Cc: linuxppc-dev@lists.ozlabs.org
> >> Cc: Arnd Bergmann <arnd@arndb.de>
> >> Cc: "Pali Rohár" <pali@kernel.org>
> >> ---
> >>  arch/powerpc/kernel/udbg.c |    1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff -- a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c
> >> --- a/arch/powerpc/kernel/udbg.c
> >> +++ b/arch/powerpc/kernel/udbg.c
> >> @@ -14,6 +14,7 @@
> >>  #include <asm/udbg.h>
> >>  
> >>  void (*udbg_putc)(char c);
> >> +EXPORT_SYMBOL(udbg_putc);
> >>  void (*udbg_flush)(void);
> >>  int (*udbg_getc)(void);
> >>  int (*udbg_getc_poll)(void);
> > 
> > Hello! I do not think that it is a good idea to export udbg functions
> > for kernel modules. I have quickly looked at the cpm_uart driver file
> 
> Sure, that was just a conversation starter.
> 
> > drivers/tty/serial/cpm_uart/cpm_uart_core.c and it looks like that once
> > udbg from it is registered then there is no code for unregistering it.
> > So I have feeling that compiling cpm_uart driver as module should not be
> > allowed when CONFIG_SERIAL_CPM_CONSOLE is enabled, and early debug
> > should depend on CONFIG_CONSOLE_POLL || CONFIG_SERIAL_CPM_CONSOLE.
> 
> The other change above also fixes the build error: (Option 2)
> 
> >> config PPC_EARLY_DEBUG_CPM
> >> 	bool "Early serial debugging for Freescale CPM-based serial ports"
> >> -	depends on SERIAL_CPM
> >> +	depends on SERIAL_CPM=y
> 
> 
> Also, making SERIAL_CPM (cpm_uart driver) be restricted to not allow it
> as a module when SERIAL_CPM_CONSOLE is enabled [how does one express that
> in Kconfig language?] will cause a circular dependency since SERIAL_CPM_CONSOLE
> depends on SERIAL_CPM=y. It looks like you are suggesting reversing the
> dependencies.

I see that SERIAL_CPM_CONSOLE has already "depends on SERIAL_CPM=y".
Am I right that this already disallow compiling cpm_uart driver as
module when SERIAL_CPM_CONSOLE is enabled?

> > Any other opinion?
> 
> Yes, please. Otherwise I prefer my option 2.
> 
> -- 
> ~Randy

Option 2 looks like a better solution.
  

On 5/13/23 16:05, Pali Rohár wrote:
> On Saturday 13 May 2023 15:53:19 Randy Dunlap wrote:
>> Hi Pali,
>>
>> On 5/13/23 02:13, Pali Rohár wrote:
>>> On Friday 12 May 2023 22:58:04 Randy Dunlap wrote:
>>>> In a randconfig with CONFIG_SERIAL_CPM=m and
>>>> CONFIG_PPC_EARLY_DEBUG_CPM=y, there is a build error:
>>>> ERROR: modpost: "udbg_putc" [drivers/tty/serial/cpm_uart/cpm_uart.ko] undefined!
>>>>
>>>> The build can be fixed by exporting "udbg_putc" in udbg.c.
>>>>
>>>> OTOH, maybe something like this is more appropriate in
>>>> arch/powerpc/Kconfig.debug?
>>>>
>>>> config PPC_EARLY_DEBUG_CPM
>>>> 	bool "Early serial debugging for Freescale CPM-based serial ports"
>>>> -	depends on SERIAL_CPM
>>>> +	depends on SERIAL_CPM=y
>>>>
>>>> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
>>>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>>>> Cc: Nicholas Piggin <npiggin@gmail.com>
>>>> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
>>>> Cc: linuxppc-dev@lists.ozlabs.org
>>>> Cc: Arnd Bergmann <arnd@arndb.de>
>>>> Cc: "Pali Rohár" <pali@kernel.org>
>>>> ---
>>>>  arch/powerpc/kernel/udbg.c |    1 +
>>>>  1 file changed, 1 insertion(+)
>>>>
>>>> diff -- a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c
>>>> --- a/arch/powerpc/kernel/udbg.c
>>>> +++ b/arch/powerpc/kernel/udbg.c
>>>> @@ -14,6 +14,7 @@
>>>>  #include <asm/udbg.h>
>>>>  
>>>>  void (*udbg_putc)(char c);
>>>> +EXPORT_SYMBOL(udbg_putc);
>>>>  void (*udbg_flush)(void);
>>>>  int (*udbg_getc)(void);
>>>>  int (*udbg_getc_poll)(void);
>>>
>>> Hello! I do not think that it is a good idea to export udbg functions
>>> for kernel modules. I have quickly looked at the cpm_uart driver file
>>
>> Sure, that was just a conversation starter.
>>
>>> drivers/tty/serial/cpm_uart/cpm_uart_core.c and it looks like that once
>>> udbg from it is registered then there is no code for unregistering it.
>>> So I have feeling that compiling cpm_uart driver as module should not be
>>> allowed when CONFIG_SERIAL_CPM_CONSOLE is enabled, and early debug
>>> should depend on CONFIG_CONSOLE_POLL || CONFIG_SERIAL_CPM_CONSOLE.
>>
>> The other change above also fixes the build error: (Option 2)
>>
>>>> config PPC_EARLY_DEBUG_CPM
>>>> 	bool "Early serial debugging for Freescale CPM-based serial ports"
>>>> -	depends on SERIAL_CPM
>>>> +	depends on SERIAL_CPM=y
>>
>>
>> Also, making SERIAL_CPM (cpm_uart driver) be restricted to not allow it
>> as a module when SERIAL_CPM_CONSOLE is enabled [how does one express that
>> in Kconfig language?] will cause a circular dependency since SERIAL_CPM_CONSOLE
>> depends on SERIAL_CPM=y. It looks like you are suggesting reversing the
>> dependencies.
> 
> I see that SERIAL_CPM_CONSOLE has already "depends on SERIAL_CPM=y".
> Am I right that this already disallow compiling cpm_uart driver as
> module when SERIAL_CPM_CONSOLE is enabled?

No, it just prevents SERIAL_CPM_CONSOLE from being set when
SERIAL_CPM=m.

>>> Any other opinion?
>>
>> Yes, please. Otherwise I prefer my option 2.
>>
>> -- 
>> ~Randy
> 
> Option 2 looks like a better solution.

Thanks.