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

[Marc Zyngier]

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@xxxxxxxxxx> 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...