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

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Message-ID: <55A4952A.3090309@wwwdotorg.org>
Date:	Mon, 13 Jul 2015 22:50:50 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Noralf Trønnes <noralf@...nnes.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

On 07/11/2015 09:26 AM, Noralf Trønnes wrote:
> 
> 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.

What prevents a DT from (incorrectly) referencing the extra hwirqs?
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