drivers: meson: sm: correct meson_sm_* API retval handling

1. Following the ARM SMC32 calling convention, the return value
from secure monitor is a 32-bit signed integer. This patch changes
the type of the return value of the function meson_sm_call().

2. Now, when meson_sm_call() returns a 32-bit signed integer, we need
to ensure that this value is not negative. It is important to check
that the return value is not negative in both the meson_sm_call_read()
and meson_sm_call_write() functions.

3. Add a comment explaining why it is necessary to check if the SMC
return value is equal to 0 in the function meson_sm_call_read().
It is not obvious when reading this code.

Signed-off-by: Alexey Romanov <avromanov@salutedevices.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20230830140850.17130-1-avromanov@salutedevices.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/firmware/meson/meson_sm.h b/include/linux/firmware/meson/meson_sm.h
index 95b0da2326a9..8eaf8922ab02 100644
--- a/include/linux/firmware/meson/meson_sm.h
+++ b/include/linux/firmware/meson/meson_sm.h
@@ -19,7 +19,7 @@ enum {
 struct meson_sm_firmware;
 
 int meson_sm_call(struct meson_sm_firmware *fw, unsigned int cmd_index,
-		  u32 *ret, u32 arg0, u32 arg1, u32 arg2, u32 arg3, u32 arg4);
+		  s32 *ret, u32 arg0, u32 arg1, u32 arg2, u32 arg3, u32 arg4);
 int meson_sm_call_write(struct meson_sm_firmware *fw, void *buffer,
 			unsigned int b_size, unsigned int cmd_index, u32 arg0,
 			u32 arg1, u32 arg2, u32 arg3, u32 arg4);