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68f4dff099
Adds a section covering CONFIG_SENSORS_LSM6DS3TRC_FIFO: what it changes (one interrupt/I2C read per watermark instead of per sample) and its three limitations while it's on -- both sub-sensors forced to the same ODR, temperature no longer per-sample (one read per drain applied to the whole batch), and both sub-sensors must stay physically enabled regardless of subscription, since the chip's FIFO write trigger needs both running -- plus the watermark/ORB-buffer-size relationship callers need to respect. Also documents a related chip quirk found during bench testing: diff_words reads 0 at the exact moment a real FIFO overrun occurs, even though the FIFO is still completely full of valid, retained data (a forced read past that point recovers real samples, not garbage). This isn't a bug in this driver: ST's own engineers confirm the same behavior for this chip family on their community forum (thread "LSM6DS3 FIFO status clarification", td-p/184022), and the mainline Linux st_lsm6dsx driver doesn't attempt to recover from it either -- it only special-cases an empty FIFO, not an overrun one. Documenting this in a comment rather than adding recovery logic: with the small watermark this driver uses, reaching a real overrun at all means the drain has already fallen many seconds behind, and ST's own guidance for this condition is to avoid it via watermark sizing rather than recover from it. Signed-off-by: Felipe Moura <moura.fmo@gmail.com> |
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