On Fri, May 15, 2020 at 02:45:25PM +0200, Greg Kroah-Hartman wrote: > 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 <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> > > Cc: Alexey Malahov <Alexey.Malahov@xxxxxxxxxxxxxxxxxxxx> > > Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx> > > Cc: Paul Burton <paulburton@xxxxxxxxxx> > > Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> > > Cc: Arnd Bergmann <arnd@xxxxxxxx> > > Cc: Long Cheng <long.cheng@xxxxxxxxxxxx> > > Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > > Cc: Maxime Ripard <mripard@xxxxxxxxxx> > > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > > Cc: Will Deacon <will@xxxxxxxxxx> > > Cc: Russell King <linux@xxxxxxxxxxxxxxx> > > Cc: linux-mips@xxxxxxxxxxxxxxx > > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > > Cc: linux-mediatek@xxxxxxxxxxxxxxxxxxx > > --- > > 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. Ok. I guess I've just copied the line from some of the export symbol statements below. My mistake. Sorry. -Sergey > > thanks, > > greg k-h