linux-kernel - Re: [PATCH] genirq: Introduce irq_read

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Date:	Tue, 21 Oct 2014 17:14:21 -0700
From:	Feng Kan <fkan@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Andersson <bjorn@...o.se>,
	Marc Zyngier <marc.zyngier@....com>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Abhijeet Dharmapurikar <adharmap@...eaurora.org>,
	Y Vo <yvo@....com>, Tin Huynh <tnhuynh@....com>,
	patches <patches@....com>, Toan Le <toanle@....com>,
	Phong Vo <pvo@....com>
Subject: Re: [PATCH] genirq: Introduce irq_read_line()

On Tue, Oct 21, 2014 at 2:30 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Tuesday 21 October 2014 11:22:40 Thomas Gleixner wrote:
>> On Thu, 4 Sep 2014, Bjorn Andersson wrote:
>>
>> > On Tue, Aug 19, 2014 at 1:23 PM, Bjorn Andersson
>> > <bjorn.andersson@...ymobile.com> wrote:
>> > > Introduce the irq_read_line() function to allow device drivers to read
>> > > the current logical state of an input when the hardware only exposes
>> > > this through status bits in the interrupt controller.
>> > >
>> > > The new function is backed by a new callback function in the irq_chip -
>> > > irq_read_line() - that can be implemented by irq_chips that owns such
>> > > status bits.
>> > >
>> > > Based on rfc patch from April 2011 by Abhijeet.
>> > >
>> > > Cc: Abhijeet Dharmapurikar <adharmap@...eaurora.org>
>> > > Signed-off-by: Bjorn Andersson <bjorn.andersson@...ymobile.com>
>> >
>> > ping?
>>
>> Sorry, slipped through the cracks. I was talking about this to Marc
>> last week and he needs it for yet another reason. He had some thoughts
>> about the state representation, so I wait for him to comment.
>
> I looked up my older email as well and found which gpio driver had the
> requirement to get the irq status from the upstream controller. It was
> "gpio: Add APM X-Gene standby GPIO controller driver". I'm adding the
> APM developers on Cc here so they can participate in the discussion.
>
> As a brief summary: APM have a GPIO driver that needs to read the status
> from the ARM GIC in order to implement gpio_get_value.

Thanks, we will rebase our standby gpio patch on top of this change.

 The KVM hypervisor
> needs multiple bits from the GIC in order to implement suspend/resume,
> and Qualcomm MSM (as Bjorn wrote above) also needs to expose the status
> of the IRQ line like APM does.
>
> These should all use the same interface for the interrupt controller,
> but the interface still needs to be added.
>
>         Arnd
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