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

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Message-ID: <CAPY8ntCG3vLy1NWNF09DEZWE-t_xc+q5m89Jv8GB8GofBLVp3Q@mail.gmail.com>
Date:   Wed, 10 Feb 2021 15:49:03 +0000
From:   Dave Stevenson <dave.stevenson@...pberrypi.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Maxime Ripard <maxime@...no.tech>,
        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 Marc.

On Wed, 10 Feb 2021 at 15:30, Marc Zyngier <maz@...nel.org> wrote:
>
> 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... :-/

Thanks for the info.

Option 3 - remove l2-intc and drop back to polling the i2c-brcmstb
blocks (which the driver supports anyway).
HDMI I2C generally isn't heavily used once displays are connected, so
I'd be OK with that.

(We can keep the l2-intc that handles CEC and HPD as that is on a
unique GIC interrupt).

  Dave