[spi_device] Remove Generic (a.k.a. FwMode) from SPI_DEVICE HWIP

[eunchan]

This is a topic brought up multiple times. As TPM can behave almost identical but limited frame size (64B in TPM vs 1kB or more), it is OK to remove Generic mode. TPM protocol, however, has better flow control compared to Generic mode.

The benefit of removing Generic mode is to clean up the complex CDC path on SRAM B port in SPI_DEVICE. It raises many CDC warnings and errors, so that we waived many of them. By removing the Generic mode, SRAM b datapath sits in SPI_CLK always, which simplifies the clock domain and makes easier to verify CDC.

CC: @tjaychen @weicaiyang @jeoongp

[a-will]

The benefit of removing Generic mode is to clean up the complex CDC path on SRAM B port in SPI_DEVICE. It raises many CDC warnings and errors, so that we waived many of them. By removing the Generic mode, SRAM b datapath sits in SPI_CLK always, which simplifies the clock domain and makes easier to verify CDC.

I'll point out that adjusting the generic mode logic so it doesn't use asynchronous FIFOs in front of the SRAM would also take care of that issue. Removing generic mode altogether may be the best choice, but it's not the only way to get rid of the complex CDC.

[eunchan]

Yep. you are right. We can fix the issue as DPRPAM now supports byte enable (it wasn't when GenericMode was designed. That's why DPSRAM was in SYS_CLK and async fifo was there). But as I mentioned, it is not worth to have two almost identical modules in SPI_DEVICE.

[tjaychen]

if we remove generic mode, does that mean spi device would have no way of constructing a full duplex protocol if someone wanted to use it that way?

[eunchan]

You are right. Hum.. TPM cannot replace the Generic mode fully. Thanks for pointing it out. Totally forgot that :) If we need that, indeed we should keep Generic mode and async FIFO.

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On Oct 13, 2022, at 9:57 AM, tjaychen ***@***.***> wrote: if we remove generic mode, does that mean spi device would have no way of constructing a full duplex protocol if someone wanted to use it that way? — Reply to this email directly, view it on GitHub <#15452 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAJDG3TLPG7Y6XAWWBTK4UDWDA5ONANCNFSM6AAAAAARDUBVUQ>. You are receiving this because you were assigned.

[tjaychen]

i've honestly only ever seen 2 use cases of someone doing that.
@a-will may have seen others.

[andreaskurth]

Triaged for spi_device. Labeling Type:FutureRelease Not relevant to currently planned releases/milestones because removing Generic / FW mode seems out of scope for this release. Verification of the mentioned CDC path is tracked in #15457.

[msfschaffner]

Indeed, removing / changing generic mode is out of scope for M2.5.
CDC will be closed separately as noted above.