K 10
svn:author
V 3
avg
K 8
svn:date
V 27
2019-10-22T14:20:35.722668Z
K 7
svn:log
V 1294
nctgpio: improve performance (latency) of operation

This change consists of two parts.

First, nctgpio now supports hardware access via an I/O port window if
it's configured by firmware.  For instance, PC Engines firmware
v4.10.0.2 does that.  This is faster than going through the Super I/O
configuration registers.

Second, nctgpio now caches values of bits that it controls.  For
example, the driver does not need to access the hardware to determine if
a pin is an output or an input, or a state of an output.  Also, the
driver makes use of the fact that the hardware preserves an output state
of a pin accross a switch to the input mode and back.

With this change I am able to use the 1-Wire bus over nctgpio whereas
previously the driver introduced too much latency to be compliant with
the relatively strict protocol timings.

superio0: <Nuvoton NCT5104D/NCT6102D/NCT6106D (rev. B+)> at port 0x2e-0x2f on isa0
gpio1: <Nuvoton GPIO controller> at GPIO ldn 0x07 on superio0
pcib0: allocated type 4 (0x220-0x226) for rid 0 of gpio1
gpiobus1: <GPIO bus> on gpio1
owc0: <GPIO attached one-wire bus> at pin 4 on gpiobus1
ow0: <1 Wire Bus> on owc0
ow0: romid 28:b2:9e:45:92:10:02:34: no driver
ow_temp0: <Advanced One Wire Temperature> romid 28:b2:9e:45:92:10:02:34 on ow0

MFC after:	4 weeks

END