serial: max310x: fix RS485 delays being programmed as bit-times

The HDPIXDELAY register counts the RTS setup and hold delays in
bit-times, four bits per direction, but the driver has been writing the
struct serial_rs485 delay_rts_before_send/delay_rts_after_send values
into it unconverted - and the uapi expresses those in milliseconds. A
requested 9 ms setup delay is programmed as 9 bit-times, which at 9600
baud is 0.94 ms, roughly a tenth of what userspace asked for; the error
grows with the baud rate.

Cache the baud rate in set_termios() and convert the delays to
bit-times at the current rate, rounding up so the delay on the wire is
never shorter than requested, and capping at the 15 bit-times the
4-bit field can hold. The conversion lives in
max310x_set_rts_ctl_params(); set_termios() now calls it as well,
since the conversion depends on the baud rate.

The delays a 4-bit bit-time field can represent still fall well short
of the milliseconds the uapi can express; requests beyond 15 bit-times
are capped, and the -ERANGE rejection of values above 15 ms remains in
place for now.

Fixes: 55367c620aed ("serial: max310x: Add support for RS-485 mode")
Assisted-by: Claude:claude-fable-5
Signed-off-by: Tapio Reijonen <tapio.reijonen@vaisala.com>
Link: https://patch.msgid.link/20261008-max310x-rs485-sw-delay-v8-4-6ba881f81e1f@vaisala.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions