From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Anton Vorontsov <anton.vorontsov@linaro.org>
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 20:18:10 +0100 [thread overview]
Message-ID: <20120910201810.409a58ea@pyramind.ukuu.org.uk> (raw)
In-Reply-To: <20120910175725.GA13673@lizard>
> > 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.
Can you use test_bit() as well. I'm trying to gradually push all the code
that way so people habitually use set_bit() and we don't get any (more)
races where some compile situations and architectures otherwise create
load to register
register ored with constant
write back
> 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()).
One of the long term goals of tty_port has always ben to have an object
with the lifetime of the physical port so this kind of thing can be fixed.
> 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.
Agreed - however you'll need a separate refcount than the main tty one
for this, because we still need to do a hangup() on the final "tty" close
even if the hardware is 'pinned' for a debugger.
Alan
WARNING: multiple messages have this Message-ID (diff)
From: alan@lxorguk.ukuu.org.uk (Alan Cox)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 06/14] tty/serial/core: Introduce poll_init callback
Date: Mon, 10 Sep 2012 20:18:10 +0100 [thread overview]
Message-ID: <20120910201810.409a58ea@pyramind.ukuu.org.uk> (raw)
In-Reply-To: <20120910175725.GA13673@lizard>
> > 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.
Can you use test_bit() as well. I'm trying to gradually push all the code
that way so people habitually use set_bit() and we don't get any (more)
races where some compile situations and architectures otherwise create
load to register
register ored with constant
write back
> 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()).
One of the long term goals of tty_port has always ben to have an object
with the lifetime of the physical port so this kind of thing can be fixed.
> 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.
Agreed - however you'll need a separate refcount than the main tty one
for this, because we still need to do a hangup() on the final "tty" close
even if the hardware is 'pinned' for a debugger.
Alan
next prev parent reply other threads:[~2012-09-10 19:13 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
2012-09-10 17:57 ` Anton Vorontsov
2012-09-10 19:18 ` Alan Cox [this message]
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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