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From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Serge Semin <fancer.lancer@gmail.com>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Jiri Slaby <jslaby@suse.com>,
	Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
	Paul Burton <paulburton@kernel.org>,
	Ralf Baechle <ralf@linux-mips.org>, Arnd Bergmann <arnd@arndb.de>,
	Long Cheng <long.cheng@mediatek.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Russell King <linux@armlinux.org.uk>,
	<linux-mips@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-mediatek@lists.infradead.org>,
	Lukas Wunner <lukas@wunner.de>, Stefan Roese <sr@denx.de>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Allison Randal <allison@lohutok.net>,
	Yegor Yefremov <yegorslists@googlemail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Dmitry Safonov <0x7f454c46@gmail.com>,
	<linux-serial@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 2/4] serial: 8250: Add 8250 port clock update method
Date: Fri, 15 May 2020 17:32:54 +0300
Message-ID: <20200515143254.oicqdkvvh6zkuqyl@mobilestation> (raw)
In-Reply-To: <20200515124525.GA1888557@kroah.com>

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@baikalelectronics.ru>
> > Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
> > Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> > Cc: Paul Burton <paulburton@kernel.org>
> > Cc: Ralf Baechle <ralf@linux-mips.org>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Long Cheng <long.cheng@mediatek.com>
> > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > Cc: Maxime Ripard <mripard@kernel.org>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Russell King <linux@armlinux.org.uk>
> > Cc: linux-mips@vger.kernel.org
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: linux-mediatek@lists.infradead.org
> > ---
> >  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

  reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200306130231.05BBC8030795@mail.baikalelectronics.ru>
     [not found] ` <20200306134049.86F8180307C2@mail.baikalelectronics.ru>
     [not found]   ` <20200310001444.B0F50803087C@mail.baikalelectronics.ru>
2020-03-10 14:17     ` [PATCH] serial: 8250_dw: Fix common clocks usage race condition Andy Shevchenko
     [not found]     ` <20200310141715.7063280307CA@mail.baikalelectronics.ru>
2020-03-12 18:47       ` Sergey Semin
2020-03-18 15:19         ` Andy Shevchenko
2020-03-23  2:46 ` [PATCH v2] " Sergey.Semin
2020-03-23  9:20   ` Andy Shevchenko
2020-03-23 11:11     ` Sergey Semin
2020-03-23 11:52       ` Andy Shevchenko
2020-03-23 17:07         ` Sergey Semin
2020-03-23 10:01   ` Maxime Ripard
2020-03-23 13:50     ` Sergey Semin
2020-03-24  9:41       ` Maxime Ripard
2020-03-24 10:12       ` Andy Shevchenko
2020-03-25 17:11         ` Sergey Semin
2020-03-26  1:44           ` Stephen Boyd
2020-03-27  9:12             ` Sergey Semin
2020-05-06 23:31   ` [PATCH v3 0/4] serial: 8250_dw: Fix ref clock usage Serge Semin
2020-05-06 23:31     ` [PATCH v3 1/4] serial: 8250: Fix max baud limit in generic 8250 port Serge Semin
2020-05-15 13:48       ` Andy Shevchenko
2020-05-06 23:31     ` [PATCH v3 2/4] serial: 8250: Add 8250 port clock update method Serge Semin
2020-05-15 12:45       ` Greg Kroah-Hartman
2020-05-15 14:32         ` Serge Semin [this message]
2020-05-06 23:31     ` [PATCH v3 3/4] serial: 8250_dw: Simplify the ref clock rate setting procedure Serge Semin
2020-05-15 14:05       ` Andy Shevchenko
2020-05-15 14:50         ` Serge Semin
2020-05-15 15:05           ` Andy Shevchenko
2020-05-06 23:31     ` [PATCH v3 4/4] serial: 8250_dw: Fix common clocks usage race condition Serge Semin
2020-05-15 14:10       ` Andy Shevchenko
2020-05-15 15:19         ` Serge Semin
2020-05-07 18:29     ` [PATCH v3 0/4] serial: 8250_dw: Fix ref clock usage Andy Shevchenko

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