linux-kernel - Re: [PATCH] irqchip: bcm2835: Add FIQ support

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Message-ID: <55A135B4.1060309@tronnes.org>
Date:	Sat, 11 Jul 2015 17:26:44 +0200
From:	Noralf Trønnes <noralf@...nnes.org>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	tglx@...utronix.de, jason@...edaemon.net,
	linux-rpi-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] irqchip: bcm2835: Add FIQ support


Den 11.07.2015 06:09, skrev Stephen Warren:
> (Sorry for the slow reply; I was on vacation)
>
> On 06/18/2015 07:32 AM, Noralf Trønnes wrote:
>> Den 18.06.2015 04:26, skrev Stephen Warren:
>>> On 06/12/2015 11:26 AM, Noralf Trønnes wrote:
>>>> Add a duplicate irq range with an offset on the hwirq's so the
>>>> driver can detect that enable_fiq() is used.
>>>> Tested with downstream dwc_otg USB controller driver.
>>> This basically looks OK, but a few comments/thoughts:
>>> b) Doesn't the driver need to refuse some operation (handler
>>> registration, IRQ setup, IRQ enable, ...?) for more than 1 IRQ in the
>>> FIQ range, since the FIQ control register only allows routing 1 IRQ to
>>> FIQ.
>> claim_fiq() protects the FIQ. See d) answer below.
> That assumes the IRQ is "accessed" via the fiq-specific APIs. Since this
> patch changes the IRQ domain from having n IRQs to having 2*n IRQs, and
> doesn't do anything special to prevent clients from using IRQs n..2n-1
> via the existing IRQ APIs, it's quite possible the a buggy client would.

Yes, but doesn't this apply to all irq use, using the wrong one doesn't 
work.
If FIQ's where in more common use, we might have seen a FIQ IRQ flag instead
of special FIQ irqs.

> (From another email):
>>>> c) The DT binding needs updating to describe the extra IRQs:
>>>>
>>>>> Documentation/devicetree/bindings/interrupt-controller/brcm,bcm28armctrl-ic.txt
>>> Ok.
>> I have seconds thoughts on this:
>> This patch does not change the DT bindings so I don't see what update
>> I should make. This patch only adds support for the Linux way of
>> handling FIQ's through enable_fiq(). It doesn't change how interrupts
>> are described in the DT.
> The intention of the patch may not be to expand the set of IRQs
> available via DT, but it does in practice. I think you need to add a
> custom of_xlate for the IRQ domain to ensure that only IRQs 0..n-1 can
> be translated from DT, and not IRQs n..2n-1. If you do that, then I
> agree that no DT binding update should be required.

armctrl_xlate() maps to the same hwirqs as before. This patch adds a
new range of hwirqs at the end of the "real" hwirq range.
It's not possible to get to these FIQ shadow hwirqs through DT.

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