linux-kernel - Re: [PATCH v4 2/3] irqchip: GIC: Add support for irq_{get,set}_irqchip

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Date:	Tue, 19 May 2015 14:45:26 -0700
From:	Feng Kan <fkan@....com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Abhijeet Dharmapurikar <adharmap@...eaurora.org>,
	Stephen Boyd <sboyd@...eaurora.org>, Phong Vo <pvo@....com>,
	Tin Huynh <tnhuynh@....com>, Y Vo <yvo@....com>,
	Thomas Gleixner <tglx@...utronix.de>, Toan Le <toanle@....com>,
	Bjorn Andersson <bjorn@...o.se>,
	Jason Cooper <jason@...edaemon.net>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Alexandre Courbot <gnurou@...il.com>
Subject: Re: [PATCH v4 2/3] irqchip: GIC: Add support for irq_{get,set}_irqchip_state

On Tue, May 19, 2015 at 3:01 AM, Marc Zyngier <marc.zyngier@....com> wrote:
> On Tue, 19 May 2015 09:40:21 +0100
> Linus Walleij <linus.walleij@...aro.org> wrote:
>
>> On Thu, May 14, 2015 at 10:14 PM, Feng Kan <fkan@....com> wrote:
>> > On Thu, May 14, 2015 at 3:32 AM, Linus Walleij <linus.walleij@...aro.org> wrote:
>>
>> >> But surely the GPIO block has its own status register, so are
>> >> you saying that this register is unreliable?
>> >
>> > When the GPIO is used as interrupt, the gpio block does not report the
>> > status anymore. Which leaves us stuck with SPISR.
>> >>
>> >> I can think of a few reasons, like transient IRQs etc but
>> >> what is actually causing this?
>> >
>> > I won't say the obvious.
>>
>> Yeah I see your problem now :(
>>
>> I think it's better to fix the access functions so that you can
>> cross-call to the GIC driver to get the SPISR flag out though.
>> Let's see what Marc says.
>>
>> >> Which GPIO driver is this? Is it upstream?
>> >
>> > Yes, it is upstream. It is the xgene slimpro gpio driver. I am starting to
>> > think that we ought to switch to use some gpio poll driver rather than
>> > using gpio-key.
>>
>> There is both gpio_keys_polled and IRQ-driven gpio_keys so yeah
>> that's possible. But honestly I think it's better to deal with this
>> problem for real because IRQ is more efficient.
>>
>> So the way I perceive it this is the real problem:
>>
>> +static int gic_irq_get_irqchip_state(struct irq_data *d,
>> +                                     enum irqchip_irq_state which, bool *val)
>> +{
>> +       switch (which) {
>> (...)
>> +       case IRQCHIP_STATE_ACTIVE:
>> +               *val = gic_peek_irq(d, GIC_DIST_ACTIVE_SET);
>> +               break; case: read
>> from 0xd04 (SPISR) instead, because that makes more
>> sense to me, or am I wrong at it?
>>
>> +       case IRQCHIP_STATE_LINE_LEVEL:
>> +               *val = gic_peek_irq(d, GIC_DIST_SPISR);
>> +               break;
>>
>> And then put a define into <linux/irqchip/arm-gic.h> for
>> GIC_DIST_SPISR.
>
> What worries me here is that the PENDING state should already give you
> the right level of information (this is what the GIC-400 TRM says). The
> only reason why SPISR exists is that software can write to the PENDING
> register, while SPISR is RO.
>
> If reading the pending state doesn't work, then I'd like to know
> exactly *why*. Only then we can add support for LINE_LEVEL using SPISR
> (which has to be GIC-400 specific, as it is not architected).

IS_PENDING and IS_ACTIVE works fine for the ISR context. However,
the nature of the register is meant for IRQ handling and not to read
the status of a GPIO. By the time the gpio_key throws a work queue
and check the status of the PENDING register, it is no long relevant.



>
> Thanks,
>
>         M.
> --
> Jazz is not dead. It just smells funny.
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