When SERIAL_8250 and HP300 are enabled, but none of SERIAL_8250_HPDCA
and SERIAL_8250_HPAPCI is built-in:

    drivers/tty/serial/8250/8250_hp300.c:24:2: warning: #warning CONFIG_SERIAL_8250 defined but neither CONFIG_SERIAL_8250_HPDCA nor CONFIG_SERIAL_8250_HPAPCI defined, are you sure? [-Wcpp]
       24 | #warning CONFIG_SERIAL_8250 defined but neither CONFIG_SERIAL_8250_HPDCA nor CONFIG_SERIAL_8250_HPAPCI defined, are you sure?
	  |  ^~~~~~~

Fix this by reworking the Kconfig logic to make such combinations
impossible:
  - Stop enabling SERIAL_8250_HP300 by default when both SERIAL_8250 and
    HP300 are enabled,
  - Instead, let SERIAL_8250_HPDCA and SERIAL_8250_HPAPCI select
    SERIAL_8250_HP300.

Note that since commit 0cff260a42c051ee ("[SERIAL] Allow 8250 PCI, PNP,
GSC and HP300 support to be disabled"), the warning message is wrong,
and should have been s/CONFIG_SERIAL_8250/CONFIG_SERIAL_8250_HP300/.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
 drivers/tty/serial/8250/8250_hp300.c | 4 ----
 drivers/tty/serial/8250/Kconfig      | 4 ++--
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_hp300.c b/drivers/tty/serial/8250/8250_hp300.c
index 583a86d87b559ec4..30e7d09eed8ae5bf 100644
--- a/drivers/tty/serial/8250/8250_hp300.c
+++ b/drivers/tty/serial/8250/8250_hp300.c
@@ -20,10 +20,6 @@
 
 #include "8250.h"
 
-#if !defined(CONFIG_SERIAL_8250_HPDCA) && !defined(CONFIG_SERIAL_8250_HPAPCI) && !defined(CONFIG_COMPILE_TEST)
-#warning CONFIG_SERIAL_8250 defined but neither CONFIG_SERIAL_8250_HPDCA nor CONFIG_SERIAL_8250_HPAPCI defined, are you sure?
-#endif
-
 #ifdef CONFIG_SERIAL_8250_HPAPCI
 struct hp300_port {
 	struct hp300_port *next;	/* next port */
diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
index 2696c236917afddd..9b5df423606bfb80 100644
--- a/drivers/tty/serial/8250/Kconfig
+++ b/drivers/tty/serial/8250/Kconfig
@@ -159,12 +159,11 @@ config SERIAL_8250_EXAR
 
 config SERIAL_8250_HP300
 	tristate
-	depends on SERIAL_8250 && HP300
-	default SERIAL_8250
 
 config SERIAL_8250_HPDCA
 	tristate "8250 HP DCA serial support"
 	depends on SERIAL_8250 && DIO
+	select SERIAL_8250_HP300
 	help
 	  If you want to use the internal "DCA" serial ports on an HP300
 	  machine, say Y here.
@@ -172,6 +171,7 @@ config SERIAL_8250_HPDCA
 config SERIAL_8250_HPAPCI
 	tristate "8250 HP APCI serial support"
 	depends on SERIAL_8250 && HP300
+	select SERIAL_8250_HP300
 	help
 	  If you want to use the internal "APCI" serial ports on an HP400
 	  machine, say Y here.
-- 
2.43.0