Re: [PATCH v7 4/9] serial: max310x: convert RS485 delays from milliseconds to bit-times

[sashiko-bot@kernel.org]

> 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>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20261005-max310x-rs485-sw-delay-v7-0-6ae392eca08c@vaisala.com?part=4