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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>