On Thu, May 07, 2020 at 02:31:33AM +0300, Serge Semin wrote: > Some platforms can be designed in a way so the UART port reference clock > might be asynchronously changed at some point. In Baikal-T1 SoC this may > happen due to the reference clock being shared between two UART ports, on > the Allwinner SoC the reference clock is derived from the CPU clock, so > any CPU frequency change should get to be known/reflected by/in the UART > controller as well. But it's not enough to just update the > uart_port->uartclk field of the corresponding UART port, the 8250 > controller reference clock divisor should be altered so to preserve > current baud rate setting. All of these things is done in a coherent > way by calling the serial8250_update_uartclk() method provided in this > patch. Though note that it isn't supposed to be called from within the > UART port callbacks because the locks using to the protect the UART port > data are already taken in there. > > Signed-off-by: Serge Semin <[email protected]> > Cc: Alexey Malahov <[email protected]> > Cc: Thomas Bogendoerfer <[email protected]> > Cc: Paul Burton <[email protected]> > Cc: Ralf Baechle <[email protected]> > Cc: Arnd Bergmann <[email protected]> > Cc: Long Cheng <[email protected]> > Cc: Andy Shevchenko <[email protected]> > Cc: Maxime Ripard <[email protected]> > Cc: Catalin Marinas <[email protected]> > Cc: Will Deacon <[email protected]> > Cc: Russell King <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > --- > drivers/tty/serial/8250/8250_port.c | 38 +++++++++++++++++++++++++++++ > include/linux/serial_8250.h | 2 ++ > 2 files changed, 40 insertions(+) > > diff --git a/drivers/tty/serial/8250/8250_port.c > b/drivers/tty/serial/8250/8250_port.c > index 4d83c85a7389..484ff9df1432 100644 > --- a/drivers/tty/serial/8250/8250_port.c > +++ b/drivers/tty/serial/8250/8250_port.c > @@ -2628,6 +2628,44 @@ static unsigned int serial8250_get_baud_rate(struct > uart_port *port, > (port->uartclk + tolerance) / 16); > } > > +/* > + * Note in order to avoid the tty port mutex deadlock don't use the next > method > + * within the uart port callbacks. Primarily it's supposed to be utilized to > + * handle a sudden reference clock rate change. > + */ > +void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk) > +{ > + struct uart_8250_port *up = up_to_u8250p(port); > + unsigned int baud, quot, frac = 0; > + struct ktermios *termios; > + unsigned long flags; > + > + mutex_lock(&port->state->port.mutex); > + > + if (port->uartclk == uartclk) > + goto out_lock; > + > + port->uartclk = uartclk; > + termios = &port->state->port.tty->termios; > + > + baud = serial8250_get_baud_rate(port, termios, NULL); > + quot = serial8250_get_divisor(port, baud, &frac); > + > + spin_lock_irqsave(&port->lock, flags); > + > + uart_update_timeout(port, termios->c_cflag, baud); > + > + serial8250_set_divisor(port, baud, quot, frac); > + serial_port_out(port, UART_LCR, up->lcr); > + serial8250_out_MCR(up, UART_MCR_DTR | UART_MCR_RTS); > + > + spin_unlock_irqrestore(&port->lock, flags); > + > +out_lock: > + mutex_unlock(&port->state->port.mutex); > +} > +EXPORT_SYMBOL(serial8250_update_uartclk);
EXPORT_SYMBOL_GPL() please. thanks, greg k-h
