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A fetch() only lower half reads the device on demand, so its data is always available and there is never anything to wait for. The upper half did not reflect that: poll() only reported POLLIN when the descriptor was opened O_NONBLOCK, and a blocking read() waited on buffersem, which is only posted when the lower half drives notify_event from an interrupt of its own. A fetch() only sensor with no interrupt therefore never satisfied poll()/read() at all. This is not hypothetical: in the in tree nucleo-h563zi:dts configuration CONFIG_STM32_DTS_TRIGGER defaults to 0, which selects stm32_dts_fetch(), and no CONFIG_STM32_DTS_ITEN_* option is enabled, so the DTS interrupt never fires. A blocking read() on that sensor waits forever, even though stm32_dts_fetch() performs a complete software triggered measurement on its own and needs no interrupt at all. Applications had to work around this by forcing O_NONBLOCK on the descriptor themselves, see apache/nuttx-apps#3686. Drop the O_NONBLOCK special case in both paths: sensor_poll() now always reports POLLIN for a fetch only sensor and sensor_read() calls fetch() directly instead of waiting. Update the sensor_ops_s::fetch documentation, which described the old contract. With the wait gone, buffersem has no waiters left. Its only two readers were the ones removed here, both in the fetch path: the wait in sensor_read() and the nxsem_get_value() in sensor_poll(). The remaining nxsem_post() calls in sensor_push_event() and sensor_notify_event() had nothing left to wake, so drop the semaphore and those posts as well. Assisted-by: Claude:claude-sonnet-5 Signed-off-by: Felipe Moura <moura.fmo@gmail.com> |
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