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serial: mvebu-uart: correctly calculate minimal possible baudrate 

For default (x16) scheme which is currently used by mvebu-uart.c driver,
maximal divisor of UART base clock is 1023*16. Therefore there is limit for
minimal supported baudrate. This change calculate it correctly and prevents
setting invalid divisor 0 into hardware registers.

Signed-off-by: Pali Rohár <pali@kernel.org>
Fixes: 68a0db1d7d ("serial: mvebu-uart: add function to change baudrate")
Link: https://lore.kernel.org/r/20210624224909.6350-4-pali@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Pali Rohár 2021-06-25 00:49:02 +02:00 committed by Greg Kroah-Hartman
parent ecd6b010d8
commit deeaf96356
1 changed files with 8 additions and 3 deletions
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11
drivers/tty/serial/mvebu-uart.c
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@ -481,7 +481,7 @@ static void mvebu_uart_set_termios(struct uart_port *port,
struct ktermios *old) struct ktermios *old)
{ {
unsigned long flags; unsigned long flags;
unsigned int baud; unsigned int baud, min_baud, max_baud;
spin_lock_irqsave(&port->lock, flags); spin_lock_irqsave(&port->lock, flags);
@ -500,16 +500,21 @@ static void mvebu_uart_set_termios(struct uart_port *port,
port->ignore_status_mask |= STAT_RX_RDY(port) | STAT_BRK_ERR; port->ignore_status_mask |= STAT_RX_RDY(port) | STAT_BRK_ERR;
/* /*
* Maximal divisor is 1023 * 16 when using default (x16) scheme.
* Maximum achievable frequency with simple baudrate divisor is 230400. * Maximum achievable frequency with simple baudrate divisor is 230400.
* Since the error per bit frame would be of more than 15%, achieving * Since the error per bit frame would be of more than 15%, achieving
* higher frequencies would require to implement the fractional divisor * higher frequencies would require to implement the fractional divisor
* feature. * feature.
*/ */
baud = uart_get_baud_rate(port, termios, old, 0, 230400); min_baud = DIV_ROUND_UP(port->uartclk, 1023 * 16);
max_baud = 230400;
baud = uart_get_baud_rate(port, termios, old, min_baud, max_baud);
if (mvebu_uart_baud_rate_set(port, baud)) { if (mvebu_uart_baud_rate_set(port, baud)) {
/* No clock available, baudrate cannot be changed */ /* No clock available, baudrate cannot be changed */
if (old) if (old)
baud = uart_get_baud_rate(port, old, NULL, 0, 230400); baud = uart_get_baud_rate(port, old, NULL,
min_baud, max_baud);
} else { } else {
tty_termios_encode_baud_rate(termios, baud, baud); tty_termios_encode_baud_rate(termios, baud, baud);
uart_update_timeout(port, termios->c_cflag, baud); uart_update_timeout(port, termios->c_cflag, baud);