From 3f0716c604e81d8440b16d0d8f5420c4a6f3c17a Mon Sep 17 00:00:00 2001 From: Andy Shevchenko Date: Thu, 22 Jan 2026 11:19:48 +0100 Subject: [PATCH] serial: 8250_pci: Remove custom deprecated baud setting routine As comments mentioned this is old (and actually deprecated) interface to set custom baud rates. This interface has limitations as it only allows to set a single opaque value called "custom_divisor". If the HW needs more complex settings (like fractional divisor) it must somehow encode this. This is horrid interface that is very driver specific and not flexible. Meanwhile Linux has established way to set free baud rate settings via BOTHER [1]. With all this being said, remove deprecated interface for good. Link: https://stackoverflow.com/questions/12646324/how-can-i-set-a-custom-baud-rate-on-linux [1] Signed-off-by: Andy Shevchenko Link: https://patch.msgid.link/20260122102349.2395423-3-andriy.shevchenko@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- Documentation/misc-devices/oxsemi-tornado.rst | 26 +----- drivers/tty/serial/8250/8250_pci.c | 91 ++++++++----------- 2 files changed, 41 insertions(+), 76 deletions(-) diff --git a/Documentation/misc-devices/oxsemi-tornado.rst b/Documentation/misc-devices/oxsemi-tornado.rst index b33351bef6cf4..fe2e5f726c2b9 100644 --- a/Documentation/misc-devices/oxsemi-tornado.rst +++ b/Documentation/misc-devices/oxsemi-tornado.rst @@ -89,31 +89,7 @@ With the baud base set to 15625000 and the unsigned 16-bit UART_DIV_MAX limitation imposed by ``serial8250_get_baud_rate`` standard baud rates below 300bps become unavailable in the regular way, e.g. the rate of 200bps requires the baud base to be divided by 78125 and that is beyond -the unsigned 16-bit range. The historic spd_cust feature can still be -used by encoding the values for, the prescaler, the oversampling rate -and the clock divisor (DLM/DLL) as follows to obtain such rates if so -required: - -:: - - 31 29 28 20 19 16 15 0 - +-----+-----------------+-------+-------------------------------+ - |0 0 0| CPR2:CPR | TCR | DLM:DLL | - +-----+-----------------+-------+-------------------------------+ - -Use a value such encoded for the ``custom_divisor`` field along with the -ASYNC_SPD_CUST flag set in the ``flags`` field in ``struct serial_struct`` -passed with the TIOCSSERIAL ioctl(2), such as with the setserial(8) -utility and its ``divisor`` and ``spd_cust`` parameters, and then select -the baud rate of 38400bps. Note that the value of 0 in TCR sets the -oversampling rate to 16 and prescaler values below 1 in CPR2/CPR are -clamped by the driver to 1. - -For example the value of 0x1f4004e2 will set CPR2/CPR, TCR and DLM/DLL -respectively to 0x1f4, 0x0 and 0x04e2, choosing the prescaler value, -the oversampling rate and the clock divisor of 62.500, 16 and 1250 -respectively. These parameters will set the baud rate for the serial -port to 62500000 / 62.500 / 1250 / 16 = 50bps. +the unsigned 16-bit range. Maciej W. Rozycki diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c index c5a932f48f744..8da725cdf9a94 100644 --- a/drivers/tty/serial/8250/8250_pci.c +++ b/drivers/tty/serial/8250/8250_pci.c @@ -1205,60 +1205,49 @@ static unsigned int pci_oxsemi_tornado_get_divisor(struct uart_port *port, u8 tcr; int i; - /* Old custom speed handling. */ - if (baud == 38400 && (port->flags & UPF_SPD_MASK) == UPF_SPD_CUST) { - unsigned int cust_div = port->custom_divisor; - - quot = cust_div & UART_DIV_MAX; - tcr = (cust_div >> 16) & OXSEMI_TORNADO_TCR_MASK; - cpr = (cust_div >> 20) & OXSEMI_TORNADO_CPR_MASK; - if (cpr < OXSEMI_TORNADO_CPR_MIN) - cpr = OXSEMI_TORNADO_CPR_DEF; - } else { - best_squot = quot_scale; - for (i = 0; i < ARRAY_SIZE(p); i++) { - unsigned int spre; - unsigned int srem; - u8 cp; - u8 tc; - - tc = p[i][0]; - cp = p[i][1]; - spre = tc * cp; - - srem = sdiv % spre; - if (srem > spre / 2) - srem = spre - srem; - squot = DIV_ROUND_CLOSEST(srem * quot_scale, spre); - - if (srem == 0) { - tcr = tc; - cpr = cp; - quot = sdiv / spre; - break; - } else if (squot < best_squot) { - best_squot = squot; - tcr = tc; - cpr = cp; - quot = DIV_ROUND_CLOSEST(sdiv, spre); - } + best_squot = quot_scale; + for (i = 0; i < ARRAY_SIZE(p); i++) { + unsigned int spre; + unsigned int srem; + u8 cp; + u8 tc; + + tc = p[i][0]; + cp = p[i][1]; + spre = tc * cp; + + srem = sdiv % spre; + if (srem > spre / 2) + srem = spre - srem; + squot = DIV_ROUND_CLOSEST(srem * quot_scale, spre); + + if (srem == 0) { + tcr = tc; + cpr = cp; + quot = sdiv / spre; + break; + } else if (squot < best_squot) { + best_squot = squot; + tcr = tc; + cpr = cp; + quot = DIV_ROUND_CLOSEST(sdiv, spre); } - while (tcr <= (OXSEMI_TORNADO_TCR_MASK + 1) >> 1 && - quot % 2 == 0) { + } + while (tcr <= (OXSEMI_TORNADO_TCR_MASK + 1) >> 1 && + quot % 2 == 0) { + quot >>= 1; + tcr <<= 1; + } + while (quot > UART_DIV_MAX) { + if (tcr <= (OXSEMI_TORNADO_TCR_MASK + 1) >> 1) { quot >>= 1; tcr <<= 1; - } - while (quot > UART_DIV_MAX) { - if (tcr <= (OXSEMI_TORNADO_TCR_MASK + 1) >> 1) { - quot >>= 1; - tcr <<= 1; - } else if (cpr <= OXSEMI_TORNADO_CPR_MASK >> 1) { - quot >>= 1; - cpr <<= 1; - } else { - quot = quot * cpr / OXSEMI_TORNADO_CPR_MASK; - cpr = OXSEMI_TORNADO_CPR_MASK; - } + } else if (cpr <= OXSEMI_TORNADO_CPR_MASK >> 1) { + quot >>= 1; + cpr <<= 1; + } else { + quot = quot * cpr / OXSEMI_TORNADO_CPR_MASK; + cpr = OXSEMI_TORNADO_CPR_MASK; } } -- 2.47.3