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From: Finn Thain <fthain@telegraphics.com.au>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Stephen N Chivers <schivers@csc.com.au>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	John Stultz <john.stultz@linaro.org>,
	linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 13/13] m68k: mvme16x: Convert to clocksource API
Date: Wed, 14 Nov 2018 09:04:36 +1100 (AEDT)
Message-ID: <alpine.LNX.2.21.1811132137180.371@nippy.intranet> (raw)
In-Reply-To: <alpine.LNX.2.21.1811130826260.356@nippy.intranet>

On Tue, 13 Nov 2018, I wrote:

> On Mon, 12 Nov 2018, Thomas Gleixner wrote:
> 
> > > +static u32 clk_total;
> > > +
> > > +#define PCC_TIMER_CLOCK_FREQ 1000000
> > > +#define PCC_TIMER_CYCLES     (PCC_TIMER_CLOCK_FREQ / HZ)
> > > +
> > >  static irqreturn_t mvme16x_timer_int (int irq, void *dev_id)
> > >  {
> > > +    irq_handler_t tick_handler = dev_id;
> > > +    unsigned long flags;
> > > +
> > > +    local_irq_save(flags);
> > 
> > No need for local_irq_save() here. Interrupt handlers are guaranteed to be
> > called with interrupts disabled.
> > 
> 
> That's not the case on m68k, as I understand it. However, the CPU 
> interrupt level does prevent interrupt handlers from nesting.
> 

What I mean by that is, the interrupt level (IPL) prevents interrupt 
handlers from being re-entered. But a handler can still get interrupted by 
a higher priority interrupt request. In the past I've had to add defensive 
locking because of this.

In these patches I've assumed it was possible for some higher priority 
interrupt handler to perform a clocksource read after the timer handler 
started executing. Hence the use of local_irq_save/restore.

To be sure, I've just run a quick test and confirmed that the timer 
handler can indeed get interrupted by the ethernet interrupt handler.

-- 

  reply index

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-12  4:12 [RFC PATCH 00/13] m68k: Drop arch_gettimeoffset and adopt " Finn Thain
2018-11-12  4:12 ` [RFC PATCH 08/13] m68k: atari: Convert to " Finn Thain
2018-11-12  4:12 ` [RFC PATCH 04/13] m68k: mac: Clean up unused timer definitions Finn Thain
2018-11-12  4:12 ` [RFC PATCH 10/13] m68k: hp300: Convert to clocksource API Finn Thain
2018-11-12  4:12 ` [RFC PATCH 11/13] m68k: mac: " Finn Thain
2018-11-12  4:12 ` [RFC PATCH 01/13] arm: Fix mutual exclusion in arch_gettimeoffset Finn Thain
2018-11-12  8:34   ` Christoph Hellwig
2018-11-13  3:39     ` Finn Thain
2018-11-13  9:20       ` Russell King - ARM Linux
2018-11-13 21:55         ` Finn Thain
2018-11-13 23:43           ` Russell King - ARM Linux
2018-11-14  1:35             ` Michael Schmitz
2018-11-14  7:58               ` Russell King - ARM Linux
2018-11-15  1:34                 ` Michael Schmitz
2018-11-14  3:17             ` Finn Thain
2018-11-14 14:16               ` Russell King - ARM Linux
2018-11-14 14:58                 ` Geert Uytterhoeven
2018-11-14 18:11                   ` Russell King - ARM Linux
2018-11-15  4:12                 ` Finn Thain
2018-11-16 17:47                   ` Russell King - ARM Linux
2018-11-16 22:49                     ` Finn Thain
2018-11-17  3:00                       ` Michael Schmitz
2018-11-14 12:05   ` Russell King - ARM Linux
2018-11-12  4:12 ` [RFC PATCH 02/13] m68k: " Finn Thain
2018-11-12  4:12 ` [RFC PATCH 07/13] m68k: amiga: Convert to clocksource API Finn Thain
2018-11-12  9:02   ` Geert Uytterhoeven
2018-11-12  9:21     ` Finn Thain
2018-11-12  4:12 ` [RFC PATCH 09/13] m68k: bvme6000: " Finn Thain
2018-11-12  4:12 ` [RFC PATCH 06/13] m68k: Drop ARCH_USES_GETTIMEOFFSET Finn Thain
2018-11-12  9:00   ` Geert Uytterhoeven
2018-11-12  9:06     ` Finn Thain
2018-11-13  2:29       ` Michael Schmitz
2018-11-13  3:14         ` Finn Thain
2018-11-13  4:50           ` Michael Schmitz
2018-11-13  6:15             ` Finn Thain
2018-11-13  8:24               ` Michael Schmitz
2018-11-13 22:11                 ` Finn Thain
2018-11-14  1:08                   ` Michael Schmitz
2018-11-14  2:58                     ` Michael Schmitz
2018-11-14 23:54                       ` Michael Schmitz
2018-11-15  4:37                         ` Finn Thain
2018-11-15  6:35                         ` Michael Schmitz
2018-11-16  0:04                           ` Finn Thain
2018-11-12  4:12 ` [RFC PATCH 13/13] m68k: mvme16x: Convert to clocksource API Finn Thain
2018-11-12 18:37   ` Thomas Gleixner
2018-11-13  0:11     ` Finn Thain
2018-11-13 22:04       ` Finn Thain [this message]
2018-11-13 22:10         ` [RFC PATCH 13/13] m68k: mvme16x: Convert to clocksource APIy Thomas Gleixner
2018-11-13 22:33           ` Finn Thain
2018-11-18 17:12             ` Thomas Gleixner
2018-11-12  4:12 ` [RFC PATCH 03/13] m68k: mac: Fix VIA timer counter accesses Finn Thain
2018-11-12  4:12 ` [RFC PATCH 12/13] m68k: mvme147: Convert to clocksource API Finn Thain
2018-11-12  4:12 ` [RFC PATCH 05/13] m68k: apollo, q40, sun3, sun3x: Remove arch_gettimeoffset implementations Finn Thain

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