[PATCH] powerpc/legacy_serial: check CONFIG_SERIAL_8250_CONSOLE

[Uwe Kleine-König]

Hello Randy,

On Thu, Jun 08, 2023 at 05:33:28PM -0700, Randy Dunlap wrote:
> When SERIAL_8250_CONSOLE is not set but PPC_UDBG_16550=y,
> the legacy_serial code references fsl8250_handle_irq, which is
> only built when SERIAL_8250_CONSOLE is set.
> 
> Be consistent in referencing the used CONFIG_SERIAL_8250*
> symbols so that the build errors do not happen.
> 
> Prevents these build errors:
> 
> powerpc-linux-ld: arch/powerpc/kernel/legacy_serial.o: in function `serial_dev_init':
> legacy_serial.c:(.init.text+0x2aa): undefined reference to `fsl8250_handle_irq'
> powerpc-linux-ld: legacy_serial.c:(.init.text+0x2b2): undefined reference to `fsl8250_handle_irq'
> 
> Fixes: 66eff0ef528b ("powerpc/legacy_serial: Warn about 8250 devices operated without active FSL workarounds")
> Signed-off-by: Randy Dunlap <rdunlap at infradead.org>
> Cc: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Cc: linux-serial at vger.kernel.org
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Cc: Nicholas Piggin <npiggin at gmail.com>
> Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
> Cc: linuxppc-dev at lists.ozlabs.org
> ---
>  arch/powerpc/kernel/legacy_serial.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff -- a/arch/powerpc/kernel/legacy_serial.c b/arch/powerpc/kernel/legacy_serial.c
> --- a/arch/powerpc/kernel/legacy_serial.c
> +++ b/arch/powerpc/kernel/legacy_serial.c
> @@ -508,9 +508,9 @@ static void __init fixup_port_irq(int in
>  
>  	port->irq = virq;
>  
> -	if (IS_ENABLED(CONFIG_SERIAL_8250) &&
> +	if (IS_ENABLED(CONFIG_SERIAL_8250_CONSOLE) &&
>  	    of_device_is_compatible(np, "fsl,ns16550")) {
> -		if (IS_REACHABLE(CONFIG_SERIAL_8250)) {
> +		if (IS_REACHABLE(CONFIG_SERIAL_8250_CONSOLE)) {
>  			port->handle_irq = fsl8250_handle_irq;
>  			port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_8250_CONSOLE);
>  		} else {

Argh, indeed there is a problem. Your patch however defeats the idea of
66eff0ef528b[1] which is still valid. And with your patch the else
branch that starts at the end of the above hunk is never taken.

With the feedback I got on
https://lore.kernel.org/linux-serial/20230605130857.85543-3-u.kleine-koenig@pengutronix.de
the probable outcome is that CONFIG_SERIAL_8250_FSL becomes tristate and
so the fix that is more future proof and keeps the warning, looks as
follows:

diff --git a/arch/powerpc/kernel/legacy_serial.c b/arch/powerpc/kernel/legacy_serial.c
index fdbd85aafeb1..6ee65741dbd5 100644
--- a/arch/powerpc/kernel/legacy_serial.c
+++ b/arch/powerpc/kernel/legacy_serial.c
@@ -510,7 +510,7 @@ static void __init fixup_port_irq(int index,
 
 	if (IS_ENABLED(CONFIG_SERIAL_8250) &&
 	    of_device_is_compatible(np, "fsl,ns16550")) {
-		if (IS_REACHABLE(CONFIG_SERIAL_8250)) {
+		if (IS_REACHABLE(CONFIG_SERIAL_8250_FSL)) {
 			port->handle_irq = fsl8250_handle_irq;
 			port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_8250_CONSOLE);
 		} else {

This should to the right thing now (while CONFIG_SERIAL_8250_FSL is
still bool and only on if CONFIG_SERIAL_8250 is =y) and also once
CONFIG_SERIAL_8250_FSL can be =m (which would make fsl8250_handle_irq
not available for powerpc platform code).

But given that I screwed this up several times now, I will think about
this some more and do some more tests before submitting that as a proper
patch.

Best regards
Uwe

[1] Warn if the 8250 device is used but the required FSL workarounds are
not.

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |
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