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SubjectRe: [RFC PATCH] powerpc: udbg: export udbg_putc
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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.
--
~Randy

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