Re: STM32MP1 level triggered interrupts

From: Marc Zyngier <maz@kernel.org>
To: Marek Vasut <marex@denx.de>
Cc: "Alexandre Torgue" <alexandre.torgue@st.com>,
	"Patrick Delaunay" <patrick.delaunay@st.com>,
	"Maxime Coquelin" <mcoquelin.stm32@gmail.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	linux-stm32@st-md-mailman.stormreply.com,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>
Subject: Re: STM32MP1 level triggered interrupts
Date: Wed, 05 Feb 2020 11:42:46 +0000	[thread overview]
Message-ID: <dcbb8f0447f2aa75f0cec6f420310b21@kernel.org> (raw)
In-Reply-To: <5e1c419c-b141-52f6-88f1-ee3ab8219a4e@denx.de>

On 2020-01-28 18:32, Marek Vasut wrote:
> On 1/24/20 10:24 AM, Marc Zyngier wrote:
>> On 2020-01-24 09:17, Alexandre Torgue wrote:
>>> On 1/23/20 11:21 PM, Marek Vasut wrote:
>> 
>> [...]
>> 
>>>> But I still wonder, what is the purpose of the EXTImux in that SoC?
>>>> Shouldn't that permit routing GPIOs directly into GIC SPIs, which 
>>>> would
>>>> then permit detecting at least level-high interrupts ?
>>>> 
>>> 
>>> For this SoC, EXTI block detects external line edges and rises a GIC
>>> SPI interrupt. This EXTi block is mainly used to handle HW events 
>>> like
>>> buttons, clocks ... So first issue seems more to be a design issue
>>> (your design doesn't fit with MP1 datasheet).
>>> 
>>> Now, let's find a solution. I'll have a look on your proposition:
>>> "check the line in EOI callback and retrig".
>>> 
>>> Marc, this kind a solution could be acceptable on your side ?
>> 
>> It will depend on the nature of the hack you will have to put in 
>> there.
>> If it is 100% reliable, why not? Anything short of that, probably not.
> 
> I had another look into this, and what we would end up is some sort of
> phandle from exti to all the gpioX nodes in DT, would that be OK ?
> However, if we do that, then we will have the pinctrl controller (which
> has the gpio banks as subnodes) require the exti through a phandle and
> exti require the gpio banks through a phandle, so we end up with some
> sort of cyclic dependency there.
> 
> So we would need to somehow have exti lazily deal with it's gpioX
> controller phandles only when someone requests level interrupt ? That
> would probably do.

TBH, I don't have much of an opinion here. If you can deal with the 
plumbing
that's required to make this thing work reliably, then why not?

What I insist on is that the sampling/retriggering is made 100% 
reliable.
I'd prefer we don't offer the functionality if it there is any doubt 
about it.

         M.
-- 
Jazz is not dead. It just smells funny...

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