From: Anton Vorontsov <anton.vorontsov@linaro.org>
To: Alan Cox <alan@linux.intel.com>
Cc: "Colin Cross" <ccross@android.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Alan Cox" <alan@lxorguk.ukuu.org.uk>,
"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>,
"Arve Hjønnevåg" <arve@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: [RFC] tty/serial/kgdboc: Add and wire up clear_irqs callback
Date: Wed, 12 Sep 2012 03:32:05 -0700 [thread overview]
Message-ID: <20120912103202.GA26690@lizard> (raw)
In-Reply-To: <20120912104420.06a88957@bob.linux.org.uk>
On Wed, Sep 12, 2012 at 10:44:20AM +0100, Alan Cox wrote:
> > Of course, if Alan is OK with this, I'm more than OK too. :-)
>
> It may well be better.
>
> > (But the polling routines would need to clear all interrupts, not
> > just rx/tx. For example, if the controller indicated some error, and
> > nobody clears it, then we'll start reentering infinitely.)
>
> For a lot of devices and platforms you'd probably mask them instead ?
If there is no way to clear them, yes, we obviously would want to
mask them before using the port for NMI debugger. Then we'd need
three callbacks:
- mask_all_irqs_but_rx() -- used before we want to start using the port
for the NMI debugger;
- clear_rx_irq() -- (optional) clears rx IRQ for controllers that need
it;
- restore_irqs() -- unmasks interrupts that were previously masked.
If we ever encounter a case when just clearing interrupts doesn't work,
we can surely implement the above scheme... It's just so far I don't
see any need to over-design this, but again, it's your call, I told my
opinion on this, but I'll do whatever you guys like more. :-)
> > > If you use a clear_irqs callback, you can drop characters if
> > > one arrives between the last character buffer read and calling
> > > clear_irqs.
> >
> > Only if we call clear_irqs() after reading the characters, but we do
> > it before. So if new characters are available, we will reenter NMI,
> > which is OK.
>
> Recursively or not... again you get platform specific magic in places
> we don't want.
I really really don't see how this is platform-specific. All we ask the
serial driver is to quiesce its interrupt. Whether we can handle
NMIs/IRQs recursively or not is not serial driver's worry, since its
IRQ handler is not going to fire anyway. The polling routines already
gave us the power to steal/inject the data, so now we're stealing the
interrupt too.
How we use the callback is indeed platform-specific, but so is the
whole KGDB, and that knowledge is hidden there.
For serial driver it's all pretty much clear: lower the interrupt, but
don't turn off rx detection.
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: [RFC] tty/serial/kgdboc: Add and wire up clear_irqs callback
Date: Wed, 12 Sep 2012 03:32:05 -0700 [thread overview]
Message-ID: <20120912103202.GA26690@lizard> (raw)
In-Reply-To: <20120912104420.06a88957@bob.linux.org.uk>
On Wed, Sep 12, 2012 at 10:44:20AM +0100, Alan Cox wrote:
> > Of course, if Alan is OK with this, I'm more than OK too. :-)
>
> It may well be better.
>
> > (But the polling routines would need to clear all interrupts, not
> > just rx/tx. For example, if the controller indicated some error, and
> > nobody clears it, then we'll start reentering infinitely.)
>
> For a lot of devices and platforms you'd probably mask them instead ?
If there is no way to clear them, yes, we obviously would want to
mask them before using the port for NMI debugger. Then we'd need
three callbacks:
- mask_all_irqs_but_rx() -- used before we want to start using the port
for the NMI debugger;
- clear_rx_irq() -- (optional) clears rx IRQ for controllers that need
it;
- restore_irqs() -- unmasks interrupts that were previously masked.
If we ever encounter a case when just clearing interrupts doesn't work,
we can surely implement the above scheme... It's just so far I don't
see any need to over-design this, but again, it's your call, I told my
opinion on this, but I'll do whatever you guys like more. :-)
> > > If you use a clear_irqs callback, you can drop characters if
> > > one arrives between the last character buffer read and calling
> > > clear_irqs.
> >
> > Only if we call clear_irqs() after reading the characters, but we do
> > it before. So if new characters are available, we will reenter NMI,
> > which is OK.
>
> Recursively or not... again you get platform specific magic in places
> we don't want.
I really really don't see how this is platform-specific. All we ask the
serial driver is to quiesce its interrupt. Whether we can handle
NMIs/IRQs recursively or not is not serial driver's worry, since its
IRQ handler is not going to fire anyway. The polling routines already
gave us the power to steal/inject the data, so now we're stealing the
interrupt too.
How we use the callback is indeed platform-specific, but so is the
whole KGDB, and that knowledge is hidden there.
For serial driver it's all pretty much clear: lower the interrupt, but
don't turn off rx detection.
Thanks!
Anton.
next prev parent reply other threads:[~2012-09-12 10:32 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-11 9:30 [PATCH v6 0/12] KGDB/KDB FIQ (NMI) debugger Anton Vorontsov
2012-09-11 9:30 ` Anton Vorontsov
2012-09-11 9:34 ` [PATCH 01/12] kernel/debug: Mask KGDB NMI upon entry Anton Vorontsov
2012-09-11 9:34 ` Anton Vorontsov
2012-09-11 9:34 ` [PATCH 02/12] kdb: Implement disable_nmi command Anton Vorontsov
2012-09-11 9:34 ` Anton Vorontsov
2012-09-11 9:34 ` Anton Vorontsov
2012-09-11 9:34 ` [PATCH 03/12] kdb: Turn KGDB_KDB=n stubs into static inlines Anton Vorontsov
2012-09-11 9:34 ` Anton Vorontsov
2012-09-11 9:34 ` Anton Vorontsov
2012-09-11 9:34 ` [PATCH 04/12] tty/serial/core: Introduce poll_init callback Anton Vorontsov
2012-09-11 9:34 ` Anton Vorontsov
2012-09-11 9:34 ` [PATCH 05/12] tty/serial/amba-pl011: Implement " Anton Vorontsov
2012-09-11 9:34 ` Anton Vorontsov
2012-09-11 9:34 ` Anton Vorontsov
2012-09-11 9:35 ` [PATCH 06/12] tty/serial/kgdboc: Add and wire up clear_irqs callback Anton Vorontsov
2012-09-11 9:35 ` Anton Vorontsov
2012-09-11 14:15 ` Alan Cox
2012-09-11 14:15 ` Alan Cox
2012-09-12 3:32 ` [RFC] " Anton Vorontsov
2012-09-12 3:32 ` Anton Vorontsov
2012-09-12 3:42 ` Colin Cross
2012-09-12 3:42 ` Colin Cross
2012-09-12 4:06 ` Anton Vorontsov
2012-09-12 4:06 ` Anton Vorontsov
2012-09-12 4:40 ` Colin Cross
2012-09-12 4:40 ` Colin Cross
2012-09-12 7:01 ` Anton Vorontsov
2012-09-12 7:01 ` Anton Vorontsov
2012-09-12 9:44 ` Alan Cox
2012-09-12 9:44 ` Alan Cox
2012-09-12 10:32 ` Anton Vorontsov [this message]
2012-09-12 10:32 ` Anton Vorontsov
2012-09-11 9:35 ` [PATCH 07/12] tty/serial/amba-pl011: Implement " Anton Vorontsov
2012-09-11 9:35 ` Anton Vorontsov
2012-09-11 9:35 ` [PATCH 08/12] tty/serial: Add kgdb_nmi driver Anton Vorontsov
2012-09-11 9:35 ` Anton Vorontsov
2012-09-11 14:14 ` Alan Cox
2012-09-11 14:14 ` Alan Cox
2012-09-12 0:41 ` Anton Vorontsov
2012-09-12 0:41 ` Anton Vorontsov
2012-09-11 9:35 ` [PATCH 09/12] ARM: Move some macros from entry-armv to entry-header Anton Vorontsov
2012-09-11 9:35 ` Anton Vorontsov
2012-09-11 9:35 ` [PATCH 10/12] ARM: Add KGDB/KDB FIQ debugger generic code Anton Vorontsov
2012-09-11 9:35 ` Anton Vorontsov
2012-09-11 9:35 ` [PATCH 11/12] ARM: VIC: Add a couple of low-level FIQ management helpers Anton Vorontsov
2012-09-11 9:35 ` Anton Vorontsov
2012-09-11 9:35 ` [PATCH 12/12] ARM: versatile: Make able to use UART ports for KGDB FIQ debugger Anton Vorontsov
2012-09-11 9:35 ` Anton Vorontsov
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