[FEATURE] configurable FW Loading polling time per platform

[fredoh9]

MAX_WAIT_FW_LOADING variable has default value of 70 seconds, The default value was decided high to cover MTL i915 probe timeout. In normal production device, FW loading time is less than a second. It doesn't mean MAX_WAIT_FW_LOADING to waste 70 seconds for every test in every platform, it will escape the polling as soon as FW loading is done.

One concern is raised, even 10 second timeout also pretty luxury but it may hide fw loading delay regression problem. If we can configure

• MAX_WAIT_FW_LOADING=70s for MTL and newer platforms which might have same i915 driver problem,
• MAX_WAIT_FW_LOADING=10s for other platforms

And with this configurable feature we can set back 10 seconds for MTL when i915 drivers are upsteamed, in near future.

Related PRs,

• lib: start polling for fw boot complete only when sof card is not pre… #1057
• check-kmod-load-unload: remove hard-coded 10s timeout #1044

[marc-hb]

Here's an interesting datapoint.

thesofproject/sof#7698 broke the MTL build. Tests were started anyway without firmware (tracked in internal issue 139). Each test took 70s to timeout in https://sof-ci.01.org/sofpr/PR7698/build9948/devicetest

The whole PR test plan uselessly hogged 3 MTL devices for more than 200 minutes (internal issues 212 and 139)