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

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Date:	Sat, 24 Jan 2015 23:25:46 +0400
From:	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Russell King <linux@....linux.org.uk>,
	Jason Cooper <jason@...edaemon.net>,
	Linus Walleij <linus.walleij@...aro.org>,
	Andrea Adami <andrea.adami@...il.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] ARM: sa1100: use ioremapped memory to access SC registers

2015-01-24 22:24 GMT+03:00 Thomas Gleixner <tglx@...utronix.de>:
> On Sat, 24 Jan 2015, Dmitry Eremin-Solenikov wrote:
>
>> 2015-01-24 20:48 GMT+03:00 Thomas Gleixner <tglx@...utronix.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.

OK, thanks for pointing. I'll update the patchset in a few days.

-- 
With best wishes
Dmitry
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