r357614 added CTLFLAG_NEEDGIANT to make it easier to find nodes that are
still not MPSAFE (or already are but aren’t properly marked).
Use it in preparation for a general review of all nodes.
This is non-functional change that adds annotations to SYSCTL_NODE and
SYSCTL_PROC nodes using one of the soon-to-be-required flags.
Mark all obvious cases as MPSAFE. All entries that haven't been marked
as MPSAFE before are by default marked as NEEDGIANT
Approved by: kib (mentor, blanket)
Commented by: kib, gallatin, melifaro
Differential Revision: https://reviews.freebsd.org/D23718
The iicdev_writeto() function basically does scatter-gather IO by filling
in a pair of iic_msg structs to write the register address then the data
from different locations but with a single bus START/xfer/STOP sequence.
It turns out several low-level i2c controller drivers do not honor the
IIC_NOSTART flag, so the second piece of the write gets a new START on
the bus, and that confuses the ads111x chips which expect a continuous
write of 3 bytes to set a register.
A proper fix for this is to track down all the misbehaving controllers
drivers and fix them. For now this change makes this driver work again.
Also, disable the comparator by default; it's not used for anything.
The previous logic would start a measurement, and then pause_sbt() for the
averaging time currently configured in the chip. After waiting that long,
the code would blindly read the measurement register and return its value.
The problem is that the chip's idea of averaging time is based on its
internal free-running 1MHz oscillator, which may be running at a wildly
different rate than the kernel clock. If the chip's internal timer was
running slower than the kernel clock, we'd end up grabbing a stale result
from an old measurement.
The driver now still uses pause_sbt() to yield the cpu while waiting for
the measurement to complete, but after sleeping it checks the chip's status
register to ensure the measurement engine is idle. If it's not, the driver
uses a retry loop to wait a bit (5% of the original wait time) then check
again for completion.
Instances of the device can be configured using hints or FDT data.
Interfaces to reconfigure the chip and extract voltage measurements from
it are available via sysctl(8).
