[spi_device] Check if CSb deasserted in the middle of byte transfer in Generic Mode

[eunchan]

Current FwMode(GenericMode) ties fwm_rxerr to 0. The signal intended to catch the receiver error in FwMode, which is to catch the CSb de-assertion without completing the byte transfer.

I decided to icebox the feature and implement in next revisions (or removing Generic mode entirely).

This issue is to track the item.

Effort estimate by @hcallahan-lowrisc:

Note that there is a number of open issues about CSB behaviour and robustness to errors, so some estimated effort (if deemed necessary) may overlap between those issues. (#10058 #12747 #15517 #15721)

estimate 20
remaining 2023-03-23 20

[andreaskurth]

Triaged for spi_device. Assigning to M2.5 with Priority:P2 Priority: medium because even though this is about robustness in an environment with errors, we should check with the product team if the behavior of spi_device is acceptable. If yes, we can defer this to Type:FutureRelease Not relevant to currently planned releases/milestones .

[hcallahan-lowrisc]

Note that there is a number of open issues about CSB behaviour and robustness to errors, so some estimated effort (if deemed necessary) may overlap between those issues. (#10058 #12747 #15517 #15721)

estimate 20
remaining 2023-03-23 20

[moidx]

We'll evaluate the behavior in silicon and determine if there are any changes needed. Adding FutureRelease for now.

[msfschaffner]

Since we plan to deprecate generic mode, this will no longer be necessary.

CC @a-will