SPI working unpredictably when 2 different SPI devices on 2 different SPI buses are heavily used simultaneously.

[jarlamsa]

Description

SPI working unpredictably when 2 different SPI devices on 2 different SPI buses are heavily used simultaneously.

Current SPI implementation has a global mutex and a global owner pointer which are preventing using different SPI buses and peripherals simultaneously. The RF drivers under mbed-os are omitting the use of the global mutex on the SPI-class because they are very high priority and the global mutex might prevent their usage. Following fix made with @kjbracey-arm fixes the issue.
jarlamsa@3c23a74

The SPI is currently going through a large modification in #8445 and will also solve the issue.

The PR is targeting a feature branch and it is not clear when it is merged to master. This issue needs to be resolved before mbed-os 5.12 is released and is considered as a blocker if it is not resolved.

Issue request type

[ ] Question
[ ] Enhancement
[x] Bug

[ciarmcom]

Internal Jira reference: https://jira.arm.com/browse/MBOCUSTRIA-330

[deepikabhavnani]

@jarlamsa - Feel free to add the PR of proposed solution. jarlamsa/mbed-os@3c23a74

[jarlamsa]

@deepikabhavnani, unfortunately that is not a proposed solution, it is just a temporary workaround. @kjbracey-arm, do you have some proposition for the fix before the #8445 is merged?

[kjbracey]

My current suggestion is to effectively cherry-pick some of #8445 and polish it off. I can spend some time doing that. My thing is a bit better than a "work-around", but I'd really rather not add the new API it requires to enable it.