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

From: Dave Stevenson <dave.stevenson@raspberrypi.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>,
	Linux Media Mailing List <linux-media@vger.kernel.org>,
	David Airlie <airlied@linux.ie>,
	Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Eric Anholt <eric@anholt.net>,
	bcm-kernel-feedback-list@broadcom.com,
	Maxime Ripard <maxime@cerno.tech>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	Daniel Vetter <daniel.vetter@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-rpi-kernel@lists.infradead.org
Subject: Re: [PATCH v2 14/15] ARM: dts: bcm2711: Add the BSC interrupt controller
Date: Wed, 10 Feb 2021 15:49:03 +0000	[thread overview]
Message-ID: <CAPY8ntCG3vLy1NWNF09DEZWE-t_xc+q5m89Jv8GB8GofBLVp3Q@mail.gmail.com> (raw)
In-Reply-To: <9d868bf76072fee7838b6f2ff73a575c@kernel.org>

Hi Marc.

On Wed, 10 Feb 2021 at 15:30, Marc Zyngier <maz@kernel.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@cerno.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

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