Is QSPI's _acquire() necessary?

[matthew-macovsky-cypress]

Description

The QSPI driver has an _owner member and a private _acquire() function that sets _owner to this. This is similar to the SPI driver, which also has an _owner and _acquire(). However, the SPI driver uses these because it has a static array of spi_peripheral_s, each containing their own spi_t, and so it makes sense for the SPI object to need to take ownership of a particular spi_peripheral_s. The QSPI driver uses no such mechanism and stores a qspi_t directly, so is it still necessary to have a concept of ownership or acquisition in that driver?

Moreover, the first time _acquire() is called in the QSPI driver, _initialize() will be called, in turn calling qspi_init() for the second time (as it was already called in the constructor). That qspi_init() needs to be repeatedly callable on the same qspi_t is not documented in the QSPI porting documentation, unlike the Watchdog or RTC documentation that explicitly notes this requirement. Is this behavior intentional? There is a comment in the QSPI driver:

//Otherwise we may have to change mode as well, so call _acquire

but as far as I can tell, _mode is only set in the constructor, so there is never a need to update it via qspi_init().

As an aside, there is a protected function acquire() declared in QSPI.h which seems to be neither defined nor used anywhere.

Issue request type

[X] Question
[ ] Enhancement
[ ] Bug

[kjbracey]

I've noted this oddity myself, but I'm not familiar enough with QSPI to know which way to resolve it.

SPI has all that complication to present the API as one SPI object per slave, but internally dealing with multiple slaves sharing one bus and/or SPI peripheral, and handing over ownership. (At least for synchronous transfers - the asynchronous API does not cope with shared peripherals).

Either QSPI should support shared buses/peripherals like SPI does, or if it's not going to, it should be simplified to remove the remaining fragments of that shared peripheral support that were copied from SPI.

[0xc0170]

Either QSPI should support shared buses/peripherals like SPI does, or if it's not going to, it should be simplified to remove the remaining fragments of that shared peripheral support that were copied from SPI.

cc @ARMmbed/mbed-os-hal

[ciarmcom]

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