Fix CMO prefetch handling of pma uncacheable

[Jackie425]

Hi,

Based on #151, this PR proposes one possible way to handle CMO prefetch with pma.uncacheable.

The proposed behavior is:

• When cfg_enable_i = 0, fence/invalidate/flush can still be handled normally, while prefetch remains load-like and is forced to the uncacheable path, which results in an error.
• When cfg_enable_i = 1, the three other CMO operations keep their current behavior, and prefetch could also treat pma.uncacheable as Don't Care, consistent with the specification.

This change implements that interpretation by ignoring pma.uncacheable for prefetch only when the cache is enabled.

Could you please confirm whether this matches the intended behavior, or whether prefetch is intentionally expected to be treated differently from the other CMO operations?

Thanks.

[Copilot]

🟡 Changes recommended

The stage-0 st0_req_is_uncacheable change forces uncacheable when cfg_enable_i=0 for all request sources, which can unintentionally suppress scrubber cachedata reads and effectively disable ECC scrubbing while disabled.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR adjusts HPDcache control logic so that CMO prefetch ignores pma.uncacheable only when the cache is enabled, aligning behavior with the “Don’t Care” specification noted in Issue #151 and preventing prefetch from being routed to the uncacheable/error path in that mode.

Changes:

• Updates stage-0 decode of st0_req_is_uncacheable to special-case CMO prefetch when cfg_enable_i=1.
• Updates stage-1 decode of st1_req_is_uncacheable similarly, ensuring prefetch is treated as cacheable when enabled.

File summaries

File	Description
rtl/src/hpdcache_ctrl.sv	Alters stage-0 and stage-1 “uncacheable” classification to ignore pma.uncacheable for CMO prefetch when the cache is enabled.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite

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[Copilot]

🟢 Approval recommended

The change is localized, consistent across stage 0/1 decoding, and directly addresses the reported misrouting of CMO prefetch under pma.uncacheable when the cache is enabled.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0 new
• Review effort level: Lite