A same-image idle-polling discriminator

The zero-input physical capture reached Bash but no summary, with no candidate stimulus. A next comparison can remove idle entry while retaining the exact already-built Memory image. This is a diagnostic hypothesis; idle failure and useful mainline boot are UNVERIFIED.

Read-only review used realized source /nix/store/f7xg031sjb9dy3bswm5s3qjr9xwx1g02-linux-mainline-k230-uart-progress-memory-src, matching dev /nix/store/1pvqbm4r3gqcvsabgkz5wvrpxfbk5k1v-linux-riscv64-unknown-linux-gnu-7.3.0-rc5-dev and Image in the lznjjfx1 bundle. Root independently verified:

• Full .config SHA256 52e7470b108ad094dbdf88b94e3e8838564edbda9e7a015b4279012e6765c9f1; CONFIG_GENERIC_IDLE_POLL_SETUP=y appears exactly once. CONFIG_CPU_IDLE=y and CONFIG_RISCV_SBI_CPUIDLE=y are also selected (lines 565, 576, 693).
• kernel/sched/idle.c SHA256 6a478625d6d7f722c3a2142f308a4ac79a6f38ab4f97c9c859e936e0c6da1f36. Lines 40–46 register bare nohlt and set forced polling; lines 351–355 restart the tick and take the polling branch; lines 57–74 poll with local IRQs enabled.
• The linked Image contains one NUL-terminated nohlt setup string. String presence is host evidence, not proof of runtime selection.

The reviewer read drivers/soc/canaan/k230-uart-progress.c lines 99–120 and 131–185: the observer waits once for completion, while the worker sleeps between cached snapshots. kernel/sched/completion.c and kernel/time/sleep_timeout.c use scheduling timeouts; drivers/tty/n_tty.c blocks a shell read waiting for input. All three can block, making idle/wakeup a useful dependency to change. A fresh Bash prompt does not prove later timer delivery. The selected timer source drivers/clocksource/timer-riscv.c programs compare through SSTC or SBI; which path executes on this run remains UNVERIFIED.

Rejected alternative: cpuidle.off=1 alone is not the same intervention, because RISC-V’s default idle path can still execute WFI (arch/riscv/kernel/process.c lines 45–47, arch/riscv/include/asm/processor.h lines 188–190). Adding ECALL markers would introduce another firmware-output dependency. No MMIO polling, IRQ masking, affinity/priority changes, firmware replacement or new kernel build is needed for the bounded nohlt comparison.

A returned summary under polling would support idle/tick-policy dependence, not isolate WFI, timer, IRQ or firmware causation. Continued silence remains inconclusive, including possible final DBCN output blocking. Forced polling is not a proposed production power policy or ordinary-root acceptance. Keep zero candidate writes, exact qualified arguments, bounded capture and separate normal recovery proof. Land a typed controller plan before implementation.