Linux-Serial Archive on lore.kernel.org
 help / color / Atom feed
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	Serge Semin <fancer.lancer@gmail.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>,
	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,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 4/4] serial: 8250_dw: Fix common clocks usage race condition
Date: Fri, 15 May 2020 17:10:46 +0300
Message-ID: <20200515141046.GF1634618@smile.fi.intel.com> (raw)
In-Reply-To: <20200506233136.11842-5-Sergey.Semin@baikalelectronics.ru>

On Thu, May 07, 2020 at 02:31:35AM +0300, Serge Semin wrote:
> The race condition may happen if the UART reference clock is shared with
> some other device (on Baikal-T1 SoC it's another DW UART port). In this
> case if that device changes the clock rate while serial console is using
> it the DW 8250 UART port might not only end up with an invalid uartclk
> value saved, but may also experience a distorted output data since
> baud-clock could have been changed. In order to fix this lets at least
> try to adjust the 8250 port setting like UART clock rate in case if the
> reference clock rate change is discovered. The driver will call the new
> method to update 8250 UART port clock rate settings. It's done by means of
> the clock event notifier registered at the port startup and unregistered
> in the shutdown callback method.

I'm wondering if clock framework itself can provide such a notifier?

> Note 1. In order to avoid deadlocks we had to execute the UART port update
> method in a dedicated deferred work. This is due to (in my opinion
> redundant) the clock update implemented in the dw8250_set_termios()
> method.

So, and how you propose to update the clock when ->set_termios() is called?

> Note 2. Before the ref clock is manually changed by the custom
> set_termios() function we swap the port uartclk value with new rate
> adjusted to be suitable for the requested baud. It is necessary in
> order to effectively disable a functionality of the ref clock events
> handler for the current UART port, since uartclk update will be done
> a bit further in the generic serial8250_do_set_termios() function.

...

> +	struct notifier_block	clk_notifier;
> +	struct work_struct	clk_work;

Oh, this seems too much.
Perhaps, the compatible based quirk with your initial approach is much better for time being.

-- 
With Best Regards,
Andy Shevchenko



  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] " 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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200515141046.GF1634618@smile.fi.intel.com \
    --to=andriy.shevchenko@linux.intel.com \
    --cc=Alexey.Malahov@baikalelectronics.ru \
    --cc=Sergey.Semin@baikalelectronics.ru \
    --cc=arnd@arndb.de \
    --cc=catalin.marinas@arm.com \
    --cc=fancer.lancer@gmail.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=heikki.krogerus@linux.intel.com \
    --cc=jslaby@suse.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mediatek@lists.infradead.org \
    --cc=linux-mips@vger.kernel.org \
    --cc=linux-serial@vger.kernel.org \
    --cc=linux@armlinux.org.uk \
    --cc=long.cheng@mediatek.com \
    --cc=mripard@kernel.org \
    --cc=paulburton@kernel.org \
    --cc=ralf@linux-mips.org \
    --cc=tsbogend@alpha.franken.de \
    --cc=wangkefeng.wang@huawei.com \
    --cc=will@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Serial Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-serial/0 linux-serial/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-serial linux-serial/ https://lore.kernel.org/linux-serial \
		linux-serial@vger.kernel.org
	public-inbox-index linux-serial

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-serial


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git