lkml.org 
[lkml]   [2018]   [Nov]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH 13/13] m68k: mvme16x: Convert to clocksource API
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.

--

\
 
 \ /
  Last update: 2018-11-13 23:04    [W:0.089 / U:0.312 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site