github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-11-07 06:17:02 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

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

Browse Source 
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: 55367c620a ("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>
This commit is contained in:
Tapio Reijonen 2026-10-08 09:48:27 +00:00 committed by Greg Kroah-Hartman
parent 56051740bf
commit 7784d6aee5
1 changed files with 31 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
drivers/tty/serial/max310x.c
View File

@ -163,6 +163,10 @@
#define MAX310X_IRDA_IRDAEN_BIT (1 << 0) /* IRDA mode enable */
#define MAX310X_IRDA_SIR_BIT (1 << 1) /* SIR mode enable */
/* HDPIXDELAY accessor macros */
#define MAX310X_HDPIXDELAY_SETUP(val) (((val) & 0x0f) << 4)
#define MAX310X_HDPIXDELAY_HOLD(val) ((val) & 0x0f)
/* Flow control trigger level register masks */
#define MAX310X_FLOWLVL_HALT_MASK GENMASK(3, 0) /* Flow control halt level */
#define MAX310X_FLOWLVL_RES_MASK GENMASK(7, 4) /* Flow control resume level */
@ -296,6 +300,7 @@ struct max310x_one {
struct work_struct md_work;
struct work_struct rs_work;
struct regmap *regmap;
unsigned int baud;
bool tx_break; /* break_ctl() owns the transceiver */
u8 rx_buf[MAX310X_FIFO_SIZE];
@ -933,23 +938,33 @@ static void max310x_set_mctrl(struct uart_port *port, unsigned int mctrl)
}
/*
* Program the chip's RS485 RTS timing (HDPIXDELAY) and the auto
* transceiver control (MODE1) from the current configuration. The
* rs485-config worker, startup() and break_ctl()'s break-off restore
* each carried their own copy of this sequence.
* Program the chip's RS485 RTS timing. The HDPIXDELAY setup and hold fields
* count bit-times, four bits per direction, while the uapi expresses the
* delays in milliseconds: convert at the current baud rate, rounding up, and
* cap at the field maximum.
*/
static void max310x_set_rts_ctl_params(struct max310x_one *one)
{
const unsigned int max_bit_dly = 15;
struct uart_port *port = &one->port;
unsigned int delay;
unsigned int setup = 0, hold = 0;
u8 mode1 = 0;
delay = (clamp(port->rs485.delay_rts_before_send, 0U, 15U) << 4) |
clamp(port->rs485.delay_rts_after_send, 0U, 15U);
max310x_port_write(port, MAX310X_HDPIXDELAY_REG, delay);
if (port->rs485.flags & SER_RS485_ENABLED) {
/* Convert milliseconds to bit-times, rounding up. */
setup = DIV_ROUND_UP(one->baud * port->rs485.delay_rts_before_send,
MSEC_PER_SEC);
hold = DIV_ROUND_UP(one->baud * port->rs485.delay_rts_after_send,
MSEC_PER_SEC);
setup = min(setup, max_bit_dly);
hold = min(hold, max_bit_dly);
if (port->rs485.flags & SER_RS485_ENABLED)
mode1 = MAX310X_MODE1_TRNSCVCTRL_BIT;
}
max310x_port_write(port, MAX310X_HDPIXDELAY_REG,
MAX310X_HDPIXDELAY_SETUP(setup) |
MAX310X_HDPIXDELAY_HOLD(hold));
/*
* A break owns the transceiver: break_ctl() disabled auto-RTS and
@ -1105,6 +1120,13 @@ static void max310x_set_termios(struct uart_port *port,
/* Update timeout according to new baud rate */
uart_update_timeout(port, termios->c_cflag, baud);
/*
* Cache the new baud rate and reprogram the RS485 RTS delays, whose
* millisecond-to-bit-time conversion depends on it.
*/
to_max310x_port(port)->baud = baud;
max310x_set_rts_ctl_params(to_max310x_port(port));
}
static void max310x_rs_proc(struct work_struct *ws)