Re: [PATCH 3/5] ARM: sa1100: use ioremapped memory to access SC registers

Thomas Gleixner
2015-01-24T19:25:00Z

On Sat, 24 Jan 2015, Dmitry Eremin-Solenikov wrote:

> 2015-01-24 20:48 GMT+03:00 Thomas Gleixner <tglx@linutronix.de>:
> > On Thu, 15 Jan 2015, Dmitry Eremin-Solenikov wrote:
> >> static void sa1100_mask_irq(struct irq_data *d)
> >> {
> >> - ICMR &= ~BIT(d->hwirq);
> >> + u32 reg;
> >> + unsigned long flags;
> >> +
> >> + raw_spin_lock_irqsave(&lock, flags);
> >
> > What's the exact point of that lock? And how is it related to the
> > $subject of the patch?
>
> It is needed to protect ICMR register during RMW cycle, isn't it?

The original code has no protection for the RMW either.

And there is a simple reason for this. These functions are guaranteed
to be called with interrupts disabled and this is a uniprocessor
machine and it will never grow SMP support. So interrupts disabled is
serialization enough.

Thanks,

tglx