Re: [PATCH] Documentation: warn users not to use select on choice options in Kconfig

[Nicolas Schier <nsc@kernel.org>]

On Wed, Jul 15, 2026 at 11:01:49PM +0100, Julian Braha wrote:
> Hengelein's master thesis about Kconfig from 2015 wrote that 'select'
> does not work on member options inside of a 'choice'.

is this true also for 'imply'?  Adding the check to kconfig seems to be
pretty simple:

diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index b2d8d4e11e07..149d3ee59b58 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -287,6 +287,11 @@ static void sym_check_prop(struct symbol *sym)
 				    "'%s' has wrong type. '%s' only "
 				    "accept arguments of bool and "
 				    "tristate type", sym2->name, use);
+			if (sym_is_choice_value(sym2))
+				prop_warn(prop,
+				    "config symbol '%s' uses %s for '%s', "
+				    "but '%s' is a choice value", sym->name,
+				    use, sym2->name, sym2->name);
 			break;
 		case P_RANGE:
 			if (sym->type != S_INT && sym->type != S_HEX)

which currently reveals

kernel/time/Kconfig:136:warning: config symbol 'NO_HZ_FULL' uses select for 'VIRT_CPU_ACCOUNTING_GEN', but 'VIRT_CPU_ACCOUNTING_GEN' is a choice value
drivers/mtd/maps/Kconfig:104:warning: config symbol 'MTD_PHYSMAP_IXP4XX' uses select for 'MTD_CFI_BE_BYTE_SWAP', but 'MTD_CFI_BE_BYTE_SWAP' is a choice value
drivers/tee/qcomtee/Kconfig:8:warning: config symbol 'QCOMTEE' uses select for 'QCOM_TZMEM_MODE_SHMBRIDGE', but 'QCOM_TZMEM_MODE_SHMBRIDGE' is a choice value

on linux-next, with the NO_HZ_FULL also being addressed by Julian [1].

Julian, please call out if you want help for pushing these.

I am considering to prepare a patch and add it for kbuild-for-next (but
not to kbuild-next) to raise attention.


Kind regards,
Nicolas

[1]: https://lore.kernel.org/r/20260801160140.2391000-1-julianbraha@gmail.com