Hi Marc.

On Wed, 10 Feb 2021 at 15:30, Marc Zyngier [off-list ref] wrote:

Hi Maxime,

On 2021-02-10 14:40, Maxime Ripard wrote:

quoted

Hi Dave,

On Tue, Feb 09, 2021 at 09:49:05AM +0000, Dave Stevenson wrote:

quoted

On Mon, 11 Jan 2021 at 14:23, Maxime Ripard [off-list ref] wrote:

quoted

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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