Linux kernel for the Tronsmart Draco AW80 Telos (Allwinner A80, sun9i) - branch draco-aw80, based on mainline. Notes, issues and exported patches live in tiagoagueda/a80.
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Tiago Águeda
2e487726b2
The coprocessor can complete a textbook startup and still be useless. The beacon arrives, the loopback passes, the first voltage query answers correctly, and every query from about a second later returns 0 mV for every rail type. Nothing returns an error. That is not cosmetic. With the voltage service dead the coprocessor still accepts a cluster power-on request, does not raise PLL_C1, and the A15 comes up at whatever c1cpux was left at - 408 MHz, slower than an A7 - with every return code reporting success. It was originally found by benchmarking, not by reading the log. Whether it happens depends on how early the firmware is started, which in turn depends on something as incidental as whether the blob is reachable from an initramfs. The race itself is still unidentified. What does not require understanding it is noticing, because the symptom is unambiguous: re-read the CPU-B rail a second after the handshake, and if it is implausible, restart the firmware - the same reset, load, release and handshake used to start it. If every attempt fails the coprocessor is deliberately left not ready, so sunxi_arisc_get_volt() returns -EAGAIN and mc_smp refuses the cluster rather than bringing it up crippled. Four good cores beat eight bad ones. start_delay_ms makes the race reproducible on demand, which it never was before. With it at 2500 the beacon lands at 3.76 s and the failure occurs every time: [3.757] startup beacon on ch2 [3.761] coprocessor up, loopback ok; CPUB rail reads 1200 mV [4.829] voltage service dead after start 1 (CPUB reads 0 mV); restarting firmware [5.119] startup beacon on ch2 [6.179] voltage service healthy after 2 starts (CPUB 1200 mV) and the rail still reads 1200 mV ninety seconds later. One thing learned while building that reproduction, which is worse than the failure this fixes: at start_delay_ms=500 the beacon lands at 1.76 s and the board does not boot at all. Every driver needing a GPIO fails - "can't get GPIO", "Error applying setting, reverse things back" - so the MMC controllers never probe and there is no root device. Starting the coprocessor early does not merely kill its voltage service; early enough, it takes the pinctrl subsystem with it. Signed-off-by: Tiago Águeda <tiago.agueda@tiagoagueda.com> |
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