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

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Date:   Wed, 10 Feb 2021 10:49:17 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Dave Stevenson <dave.stevenson@...pberrypi.com>,
        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

On 2/10/21 7:49 AM, Dave Stevenson wrote:
> 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).

Agreed, Maxime or Nicolas do you want me to send a revert of this patch?
-- 
Florian