[PATCH v2] spi: sprd-adi: Fix probe succeeding without registering the controller

With CONFIG_HWSPINLOCK=n the of_hwspin_lock_get_id() stub returns 0
unconditionally. In sprd_adi_probe() the guard

	if (ret > 0 || (IS_ENABLED(CONFIG_HWSPINLOCK) && ret == 0))

is false for that 0, so it takes the else branch, where the switch has no
case for 0 and lands in

	default:
		return dev_err_probe(&pdev->dev, ret, "failed to find hwlock id\n");

dev_err_probe() returns its err argument unchanged, so probe logs
"failed to find hwlock id" and then returns 0, reporting success.
sprd_adi_hw_init(), the restart handler and devm_spi_register_controller()
are all skipped: the device binds but no SPI controller is ever
registered.

The hardware spinlock is optional for this controller and the -ENOENT arm
already covers "no hardware spinlock supplied". Treat the stub's 0 the
same way and continue without a lock; all four users of sadi->hwlock
already test it for NULL.

This is not reachable on production kernels. Kconfig has

	depends on HWSPINLOCK || (COMPILE_TEST && !HWSPINLOCK)

so the affected configuration exists only under COMPILE_TEST, where no
real hardware is present.

Found by smatch:
drivers/spi/spi-sprd-adi.c:560 sprd_adi_probe() warn: passing zero to 'dev_err_probe'

Fixes: f9adf61e983f ("spi: sprd: adi: Change hwlock to be optional")
Assisted-by: Claude:claude-opus-5
Reviewed-by: Baolin Wang <[email protected]>
Signed-off-by: Babanpreet Singh <[email protected]>
---
Changes in v2:
- Add the fallthrough; Baolin Wang asked for [1], and carry his
  Reviewed-by. The v1 case carried only a comment, so gcc's
  -Wimplicit-fallthrough never fired and W=1 was clean either way; this
  makes the intent explicit rather than fixing a warning.
- Trim two sentences of build-verification detail out of the changelog.

v1: https://lore.kernel.org/all/[email protected]/
[1] https://lore.kernel.org/all/[email protected]/

 drivers/spi/spi-sprd-adi.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/spi/spi-sprd-adi.c b/drivers/spi/spi-sprd-adi.c
index e7d83c16b46c..a6baaf02b3c8 100644
--- a/drivers/spi/spi-sprd-adi.c
+++ b/drivers/spi/spi-sprd-adi.c
@@ -553,6 +553,12 @@ static int sprd_adi_probe(struct platform_device *pdev)
 			return -ENXIO;
 	} else {
 		switch (ret) {
+		case 0:
+			/*
+			 * Only reachable with CONFIG_HWSPINLOCK=n, where the
+			 * of_hwspin_lock_get_id() stub returns 0.
+			 */
+			fallthrough;
 		case -ENOENT:
 			dev_info(&pdev->dev, "no hardware spinlock supplied\n");
 			break;
-- 
2.43.0