diff options
| -rw-r--r-- | Documentation/misc-devices/oxsemi-tornado.rst | 26 | ||||
| -rw-r--r-- | 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 b33351bef6cf..fe2e5f726c2b 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 <macro@orcam.me.uk> diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c index c5a932f48f74..8da725cdf9a9 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; } } |