forked from unom/punktfunk
enricobuehler
c3ecc29117
Wave-2 PW5 stage 2, on the number stage 1 just made visible. `build_dmabuf_buffers` set `SPA_PARAM_BUFFERS_dataType` and stopped there — no `SPA_PARAM_BUFFERS_buffers` at all, so the pool depth the whole zero-copy safety argument rests on was entirely the producer's choice, and we never even expressed a preference. This asks for 8 (min 2, max 16). A **Choice Range**, deliberately, not a fixed count. SPA intersects the consumer's and producer's Buffers params, so a fixed 8 against a producer that can only afford 4 empties the intersection and the link stalls in "negotiating" with no error anywhere — the exact trap that cost this codebase the entire Linux cursor channel once, when a 256^2 cursor-meta max failed to intersect Mutter's fixed 384^2 offer. With a range the producer clamps into it and negotiation still succeeds; the min stays at 2 so nothing that works today stops working. The numbers, and what they are not: 8 buffers is ~133 ms of pool at 60 Hz and ~33 ms at 240 Hz, well past the ~3-4 ms capture-to-fence latency PW3/PW4 measured, with room for a second frame in flight. 16 is a ceiling rather than a request — a 4K 4:4:4 buffer is ~25 MB, so 16 of them is ~400 MB of compositor allocation. These are the values we ASK for; what a producer actually allocates is what stage 1's census line reports, and that line is the one to trust. Scoped to the dmabuf pod only. The mappable and SHM-only builders are untouched: their consumers copy out of the buffer inside `.process`, so pool depth is not part of their correctness argument. A test pins the pod SHAPE — Choice, Range, Int children, values default-first — so a later simplification cannot quietly turn the range back into a number and take the negotiation down with it. Gates green at CI parity; on-glass negotiation on each producer is stage 2's own gate and is reported with the stage-1 census numbers.