K 10
svn:author
V 3
avg
K 8
svn:date
V 27
2021-12-17T07:32:05.100376Z
K 7
svn:log
V 1209
twsi: move handling of TWSI_CONTROL_ACK into the state machine

Previously the code set TWSI_CONTROL_ACK in twsi_transfer() based on
whether the first message had a length of one.  That was done regardless
of whether the message was a read or write and what kind of messages
followed it.
Now the bit is set or cleared while handling TWSI_STATUS_ADDR_R_ACK
state transition based on the current (read) message.

The old code did not correctly work in a scenario where a single byte
was read from an EEPROM device with two byte addressing.
For example:
    i2c -m tr -a 0x50 -d r -w 16 -o 0 -c 1 -v
The reason is that the first message (a write) has two bytes, so
TWSI_CONTROL_ACK was set and never cleared.
Since the controller did not send NACK the EEPROM sent more data resulting
in a buffer overrun.

While working on TWSI_STATUS_ADDR_R_ACK I also added support for
the zero-length read access and then I did the same for zero-length write
access.
While rare, those types of I2C transactions are completely valid and are
used by some devices.

PR:		258994

(cherry picked from commit 04622a7f21157827fe75276a4520a52d3a571a86)

Git Hash:   074248b948b6fab3ec3a84e2573201fe82190cf3
Git Author: avg@FreeBSD.org
END