soundwire: stream: Poll for DP prepare to avoid interrupt deadlock #5636
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Replace the wait_for_completion_timeout() in sdw_prep_deprep_slave_ports() with a read_poll_timeout(). The original intent of the wait_for_completion_timeout() was to wait for the port prepare interrupt. But at this time the code is holding the bus_lock, which prevents the interrupt handler from running. Because of this, the port_pre completion will not be signaled and the wait_for_completion_timeout() will always timeout. Rewriting the code to avoid taking the bus_lock carries risks, and needs careful consideration of the consequences. It is safer and simpler to replace the completion with a simple register poll. As the code is holding the bus_lock, it is already blocking other activity so consuming control channel bandwidth for polling isn't really a concern. Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
bardliao
reviewed
Jan 5, 2026
| SDW_PORT_PREP_POLL_USEC, ch_prep_timeout * USEC_PER_MSEC, | ||
| false, s_rt->slave, SDW_DPN_PREPARESTATUS(p_rt->num)); | ||
| if (ret || (val < 0) || (val & p_rt->ch_mask)) { | ||
| ret = (val < 0) ? val : -ETIMEDOUT; |
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Should we not convert ret if it is not 0? In that case val could be 0
bardliao
reviewed
Jan 5, 2026
| prep_ch.bank = bus->params.next_bank; | ||
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| if (imp_def_interrupts || !simple_ch_prep_sm || | ||
| if (imp_def_interrupts || |
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Replace the wait_for_completion_timeout() in sdw_prep_deprep_slave_ports() with a read_poll_timeout().
The original intent of the wait_for_completion_timeout() was to wait for the port prepare interrupt. But at this time the code is holding the bus_lock, which prevents the interrupt handler from running. Because of this, the port_pre completion will not be signaled and the wait_for_completion_timeout() will always timeout.
Rewriting the code to avoid taking the bus_lock carries risks, and needs careful consideration of the consequences. It is safer and simpler to replace the completion with a simple register poll.
As the code is holding the bus_lock, it is already blocking other activity so consuming control channel bandwidth for polling isn't really a concern.