On Sun, Jul 31, 2022 at 10:07 PM Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > Matti Lehtimäki <matti.lehtimaki@xxxxxxxxx> wrote: > > Based on the specification for the sensor I have and also driver used in > > Android kernel for my device (it uses a 3 x 20 ms loop) I think 20 ms is > > a good value but to be sure a slightly longer might make sense. As > > suggested in the other review comment by changing the regmap_read to > > regmap_read_poll_timeout the function doesn't always need to wait at > > least 20 ms in case first read doesn't provide the correct value, if a > > suitable shorter poll interval is used (something like 1-10 ms). > > > > However testing on my device has shown that I still need to have a loop > > or at least a retry possibility because I have noticed a rare random > > read error (-6, happens after some time not at first read) when reading > > the id from the hardware. This could be due to for example internal > > init failure of the sensor chip causing an internal reset. Because of > > this read error regmap_read_poll_timeout returns with an error and > > without retrying to read the id the sensor probe fails. > > Nasty. If you can get a confirmation that it's a possible failure on startup > from the manufacturer then I'd be happier with that justification to retry > rather than just sleep for say 30msec after power on. If the power comes from an external regulator (such as a fixed-regulator on a GPIO) it could be that the startup time for that regulator is incorrectly specified or unspecified (startup-delay-us = ... for regulator-fixed)? Else I think if the a vendor version of a driver for this HW does this quirk, that's as good indication as you will ever get from a vendor. Do you have the android driver source code? Or is it a userspace blob? Yours, Linus Walleij
