From: Anton Vorontsov <anton.vorontsov@linaro.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Russell King" <linux@arm.linux.org.uk>,
"Jason Wessel" <jason.wessel@windriver.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Alan Cox" <alan@linux.intel.com>,
"Arve Hjønnevåg" <arve@android.com>,
"Colin Cross" <ccross@android.com>,
"Brian Swetland" <swetland@google.com>,
"John Stultz" <john.stultz@linaro.org>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linaro-kernel@lists.linaro.org, patches@linaro.org,
kernel-team@android.com, kgdb-bugreport@lists.sourceforge.net,
linux-serial@vger.kernel.org
Subject: Re: [PATCH 06/14] tty/serial/core: Introduce poll_init callback
Date: Mon, 10 Sep 2012 10:57:25 -0700 [thread overview]
Message-ID: <20120910175725.GA13673@lizard> (raw)
In-Reply-To: <20120910121320.03c9dfc7@pyramind.ukuu.org.uk>
On Mon, Sep 10, 2012 at 12:13:20PM +0100, Alan Cox wrote:
> > + tport = &state->port;
> > + if (!(tport->flags & ASYNC_INITIALIZED) && port->ops->poll_init) {
> > + mutex_lock(&tport->mutex);
> > + ret = port->ops->poll_init(port);
> > + /*
> > + * We don't set ASYNCB_INITIALIZED as we only initialized the
> > + * hw, e.g. state->xmit is still uninitialized.
> > + */
> > + mutex_unlock(&tport->mutex);
> > + if (ret)
> > + return ret;
> > + }
>
> What stops a parallel open or close changing ASYNC_INITIALIZED after you
> test and before you lock ?
Yeah, I should do the whole thing under the mutex.
Not related to this particular issue, but the fact that close() can powerdown
the hardware is quite bad. Today it is always possible to use open,close
sequence on /dev/ttyXXXX, and polling would break if close() deinitializes the
hardware (e.g. via uart_change_pm()).
In console= case, serial core handles the issue via uart_console(), checking if
the port is used for console, preventing it to power down the hardware. We can
do the same, or make tty_find_polling_driver() refcount individual ports/lines.
But the issue is orthogonal to this particular patch, although needs to be
fixed some day.
Thanks!
Anton.
WARNING: multiple messages have this Message-ID (diff)
From: anton.vorontsov@linaro.org (Anton Vorontsov)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 06/14] tty/serial/core: Introduce poll_init callback
Date: Mon, 10 Sep 2012 10:57:25 -0700 [thread overview]
Message-ID: <20120910175725.GA13673@lizard> (raw)
In-Reply-To: <20120910121320.03c9dfc7@pyramind.ukuu.org.uk>
On Mon, Sep 10, 2012 at 12:13:20PM +0100, Alan Cox wrote:
> > + tport = &state->port;
> > + if (!(tport->flags & ASYNC_INITIALIZED) && port->ops->poll_init) {
> > + mutex_lock(&tport->mutex);
> > + ret = port->ops->poll_init(port);
> > + /*
> > + * We don't set ASYNCB_INITIALIZED as we only initialized the
> > + * hw, e.g. state->xmit is still uninitialized.
> > + */
> > + mutex_unlock(&tport->mutex);
> > + if (ret)
> > + return ret;
> > + }
>
> What stops a parallel open or close changing ASYNC_INITIALIZED after you
> test and before you lock ?
Yeah, I should do the whole thing under the mutex.
Not related to this particular issue, but the fact that close() can powerdown
the hardware is quite bad. Today it is always possible to use open,close
sequence on /dev/ttyXXXX, and polling would break if close() deinitializes the
hardware (e.g. via uart_change_pm()).
In console= case, serial core handles the issue via uart_console(), checking if
the port is used for console, preventing it to power down the hardware. We can
do the same, or make tty_find_polling_driver() refcount individual ports/lines.
But the issue is orthogonal to this particular patch, although needs to be
fixed some day.
Thanks!
Anton.
next prev parent reply other threads:[~2012-09-10 18:00 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-10 4:08 [PATCH v5 0/14] KGDB/KDB FIQ (NMI) debugger Anton Vorontsov
2012-09-10 4:08 ` Anton Vorontsov
2012-09-10 4:11 ` [PATCH 01/14] serial/amba-pl011: fix ages old copy-paste errors Anton Vorontsov
2012-09-10 4:11 ` Anton Vorontsov
2012-09-10 4:12 ` [PATCH 02/14] drivers/tty/serial/amba-pl0{10,11}.c: use clk_prepare_enable and clk_disable_unprepare Anton Vorontsov
2012-09-10 4:12 ` Anton Vorontsov
2012-09-10 4:12 ` [PATCH 03/14] kernel/debug: Mask KGDB NMI upon entry Anton Vorontsov
2012-09-10 4:12 ` Anton Vorontsov
2012-09-10 4:13 ` [PATCH 04/14] kdb: Implement disable_nmi command Anton Vorontsov
2012-09-10 4:13 ` Anton Vorontsov
2012-09-10 4:13 ` [PATCH 05/14] kdb: Turn KGDB_KDB=n stubs into static inlines Anton Vorontsov
2012-09-10 4:13 ` Anton Vorontsov
2012-09-10 4:13 ` [PATCH 06/14] tty/serial/core: Introduce poll_init callback Anton Vorontsov
2012-09-10 4:13 ` Anton Vorontsov
2012-09-10 11:13 ` Alan Cox
2012-09-10 11:13 ` Alan Cox
2012-09-10 17:57 ` Anton Vorontsov [this message]
2012-09-10 17:57 ` Anton Vorontsov
2012-09-10 19:18 ` Alan Cox
2012-09-10 19:18 ` Alan Cox
2012-09-10 4:13 ` [PATCH 07/14] tty/serial/amba-pl011: Implement " Anton Vorontsov
2012-09-10 4:13 ` Anton Vorontsov
2012-09-10 4:13 ` [PATCH 08/14] tty/serial/kgdboc: Add and wire up clear_irqs callback Anton Vorontsov
2012-09-10 4:13 ` Anton Vorontsov
2012-09-10 11:16 ` Alan Cox
2012-09-10 11:16 ` Alan Cox
2012-09-10 17:57 ` Anton Vorontsov
2012-09-10 17:57 ` Anton Vorontsov
2012-09-10 19:19 ` Alan Cox
2012-09-10 19:19 ` Alan Cox
2012-09-10 20:13 ` Anton Vorontsov
2012-09-10 20:13 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 09/14] tty/serial/amba-pl011: Implement " Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
2012-09-10 11:17 ` Alan Cox
2012-09-10 11:17 ` Alan Cox
2012-09-10 17:56 ` Anton Vorontsov
2012-09-10 17:56 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 10/14] tty/serial: Add kgdb_nmi driver Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
2012-09-10 11:11 ` Alan Cox
2012-09-10 11:11 ` Alan Cox
2012-09-10 17:54 ` Anton Vorontsov
2012-09-10 17:54 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 11/14] ARM: Move some macros from entry-armv to entry-header Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 12/14] ARM: Add KGDB/KDB FIQ debugger generic code Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 13/14] ARM: VIC: Add a couple of low-level FIQ management helpers Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
2012-09-10 4:14 ` [PATCH 14/14] ARM: versatile: Make able to use UART ports for KGDB FIQ debugger Anton Vorontsov
2012-09-10 4:14 ` Anton Vorontsov
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