• Théo Lebrun's avatar
    spi: cadence-qspi: remove system-wide suspend helper calls from runtime PM hooks · 959043af
    Théo Lebrun authored
    The ->runtime_suspend() and ->runtime_resume() callbacks are not
    expected to call spi_controller_suspend() and spi_controller_resume().
    Remove calls to those in the cadence-qspi driver.
    
    Those helpers have two roles currently:
     - They stop/start the queue, including dealing with the kworker.
     - They toggle the SPI controller SPI_CONTROLLER_SUSPENDED flag. It
       requires acquiring ctlr->bus_lock_mutex.
    
    Step one is irrelevant because cadence-qspi is not queued. Step two
    however has two implications:
     - A deadlock occurs, because ->runtime_resume() is called in a context
       where the lock is already taken (in the ->exec_op() callback, where
       the usage count is incremented).
     - It would disallow all operations once the device is auto-suspended.
    
    Here is a brief call tree highlighting the mutex deadlock:
    
    spi_mem_exec_op()
            ...
            spi_mem_access_start()
                    mutex_lock(&ctlr->bus_lock_mutex)
    
            cqspi_exec_mem_op()
                    pm_runtime_resume_and_get()
                            cqspi_resume()
                                    spi_controller_resume()
                                            mutex_lock(&ctlr->bus_lock_mutex)
                    ...
    
            spi_mem_access_end()
                    mutex_unlock(&ctlr->bus_lock_mutex)
            ...
    
    Fixes: 0578a6db ("spi: spi-cadence-quadspi: add runtime pm support")
    Signed-off-by: default avatarThéo Lebrun <theo.lebrun@bootlin.com>
    Link: https://msgid.link/r/20240222-cdns-qspi-pm-fix-v4-2-6b6af8bcbf59@bootlin.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
    959043af
spi-cadence-quadspi.c 53.7 KB