linux-kernel - Re: [PATCH v2 14/15] ARM: dts: bcm2711: Add the BSC interrupt controller

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Date:   Wed, 10 Feb 2021 15:30:45 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Anholt <eric@...olt.net>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        LKML <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        bcm-kernel-feedback-list@...adcom.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Subject: Re: [PATCH v2 14/15] ARM: dts: bcm2711: Add the BSC interrupt
 controller

Hi Maxime,

On 2021-02-10 14:40, Maxime Ripard wrote:
> Hi Dave,
> 
> On Tue, Feb 09, 2021 at 09:49:05AM +0000, Dave Stevenson wrote:
>> On Mon, 11 Jan 2021 at 14:23, Maxime Ripard <maxime@...no.tech> wrote:
>> >
>> > The BSC controllers used for the HDMI DDC have an interrupt controller
>> > shared between both instances. Let's add it to avoid polling.
>> 
>> This seems to have unintended side effects.
>> GIC interrupt 117 is shared between the standard I2C controllers
>> (i2c-bcm2835) and the l2-intc block handling the HDMI I2C interrupts.
>> 
>> Whilst i2c-bcm2835 requests the interrupt with IRQF_SHARED, that
>> doesn't appear to be an option for l2-intc registering as an interrupt
>> controller. i2c-bcm2835 therefore loses out and fails to register for
>> the interrupt.
>> 
>> Is there an equivalent flag that an interrupt controller can add to
>> say that the parent interrupt is shared? Is that even supported?
> 
> Indeed, it looks like setting an equivalent to IRQF_SHARED would be the
> solution, but I couldn't find anything that would allow us to in the
> irqchip code.
> 
> Marc, Thomas, is it something that is allowed?

No, not really. That's because the chained handler is actually an
interrupt flow, and not a normal handler. IRQF_SHARED acts at the wrong
level for that.

I can see two possibilities:

- the l2-intc gets turned into a normal handler, and does the demux
   from there. Horrible stuff.

- the i2c controller gets parented to the l2c-int as a fake interrupt,
   and gets called from there. Horrible stuff.

Pick your poison... :-/

         M.
-- 
Jazz is not dead. It just smells funny...