[PATCH AUTOSEL 6.17-5.4] mfd: si476x: Add GPIOLIB_LEGACY dependency

[Sasha Levin <sashal@kernel.org>]

From: Arnd Bergmann <arnd@arndb.de>

[ Upstream commit e399d779c9acf277488c5b306b71dcbc71e160ca ]

This driver uses the legacy gpiolib interfaces to get gpio
numbers from platform data:

drivers/mfd/si476x-i2c.c: In function 'si476x_core_start':
   drivers/mfd/si476x-i2c.c:133:21: error: implicit declaration of function 'gpio_is_valid'; did you mean 'uuid_is_valid'? [-Werror=implicit-function-declaration]
     133 |                 if (gpio_is_valid(core->gpio_reset))

There are no in-tree users of this driver, so nothing defines
the platform data.

Add a dependency on GPIOLIB_LEGACY for the moment to avoid the build
failure, and make sure the sound driver does not get built without the
mfd portion either pass that dependency along.

Alternatively, we could remove the mfd driver along with the radio and
sound portions.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202507231653.UFlH2dMO-lkp@intel.com/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20250808151822.536879-14-arnd@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES

- What it fixes
  - Prevents a reproducible build failure when the legacy GPIO number-
    based API is disabled. The si476x MFD core calls legacy helpers such
    as `gpio_is_valid()` and `gpio_set_value_cansleep()` in
    `drivers/mfd/si476x-i2c.c:133` and `drivers/mfd/si476x-i2c.c:200`,
    which come from `linux/gpio.h` and are only provided when
    `CONFIG_GPIOLIB_LEGACY` is enabled. With legacy interfaces fenced
    off, the build hits an implicit declaration error as reported by
    kbuild test robot.

- Why it’s needed in stable
  - The GPIO subsystem recently made legacy interfaces optional/fenced
    off, which exposed drivers still using global GPIO numbers. This
    patch is part of that follow-up hardening: it gates the si476x core
    on `GPIOLIB_LEGACY`, avoiding invalid build combinations. It is a
    pure Kconfig fix with no runtime behavior change, directly
    addressing a regression introduced by the gpiolib changes and thus a
    textbook stable backport candidate for trees that have those gpiolib
    changes.

- Scope and risk
  - Small, contained Kconfig-only change; no functional code altered.
  - No architectural changes; only dependency tightening to avoid broken
    builds.
  - No known security implications.
  - Very low regression risk: there are no in-tree users of this driver,
    and the change merely prevents selecting an invalid configuration.

- Code references
  - Legacy GPIO API use causing the build error:
    - `drivers/mfd/si476x-i2c.c:133`
    - `drivers/mfd/si476x-i2c.c:200`
  - Legacy GPIO API is only provided under `CONFIG_GPIOLIB_LEGACY`:
    - `include/linux/gpio.h:1`
  - Kconfig dependency added to ensure the MFD core only builds when
    legacy GPIO is available:
    - `drivers/mfd/Kconfig:1443` adds `depends on GPIOLIB_LEGACY` to
      `MFD_SI476X_CORE`
  - Kconfig tightening to avoid building the codec without the MFD core
    (and by extension, without legacy GPIO):
    - `sound/soc/codecs/Kconfig:1945` adds `depends on MFD_SI476X_CORE`
      to `SND_SOC_SI476X`

- Stable backport guidance
  - Apply to stable series that include the GPIO changes making legacy
    interfaces optional/fenced (e.g., the 6.17 cycle and derivatives).
    It is not needed for older stable trees where legacy GPIO interfaces
    were always available (or where `GPIOLIB_LEGACY` is not
    present/always-on).

 drivers/mfd/Kconfig      | 1 +
 sound/soc/codecs/Kconfig | 1 +
 2 files changed, 2 insertions(+)

diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 425c5fba6cb1e..6d52a3d22430f 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -1411,6 +1411,7 @@ config MFD_SEC_I2C
 config MFD_SI476X_CORE
 	tristate "Silicon Laboratories 4761/64/68 AM/FM radio."
 	depends on I2C
+	depends on GPIOLIB_LEGACY
 	select MFD_CORE
 	select REGMAP_I2C
 	help
diff --git a/sound/soc/codecs/Kconfig b/sound/soc/codecs/Kconfig
index 6d7e4725d89cd..dfe907c62604c 100644
--- a/sound/soc/codecs/Kconfig
+++ b/sound/soc/codecs/Kconfig
@@ -1902,6 +1902,7 @@ config SND_SOC_SGTL5000
 
 config SND_SOC_SI476X
 	tristate
+	depends on MFD_SI476X_CORE
 
 config SND_SOC_SIGMADSP
 	tristate
-- 
2.51.0