linux-kernel - Re: [PATCH] irqchip: vt8500: Switch to a simple write clear for Interrupt Status Register

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Message-ID: <CAFRkauCmiDr+NugoVtvBaNNAaHfxVuwN_8qx7DhJK_q8A0KK8A@mail.gmail.com>
Date:	Mon, 28 Apr 2014 11:34:46 +0800
From:	Axel Lin <axel.lin@...ics.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Tony Prisk <linux@...sktech.co.nz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] irqchip: vt8500: Switch to a simple write clear for
 Interrupt Status Register

2014-04-28 2:34 GMT+08:00 Thomas Gleixner <tglx@...utronix.de>:
> On Sun, 27 Apr 2014, Axel Lin wrote:
>
>> According to the datasheet, the attribute of Interrupt Status Register is RW0S,
>> which means:
>>       Software can read the register.
>>       Software can also "write 1 to clear". "write 0" has no effect.
>> Thus switch the read/modify/write to a simple write clear.
>>
>> A read/modify/write does not make sense for an irq status register like this,
>> since otherwise a read/modify/write can race with a device raising an interrupt
>> and then clear the pending bit unintentionally.
>
> That's right, but what you are not seeing is that this is the mask
> callback which is supposed to mask the interrupt at the interrupt
> controller level.
>
> I have a hard time to see (even without reading the data sheet) how
> clearing a potentially pending interrupt in the status register will
> mask the interrupt line.

ok, I'll send a v2 to update the commit log.
Thanks for the review.

Regards,
Axel
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