Re: STM32MP1 level triggered interrupts

From: Marek Vasut <marex@denx.de>
To: Marc Zyngier <maz@kernel.org>
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, 5 Feb 2020 12:53:56 +0100	[thread overview]
Message-ID: <760b42cd-0fc4-5675-3f55-40edfe9440b2@denx.de> (raw)
In-Reply-To: <dcbb8f0447f2aa75f0cec6f420310b21@kernel.org>

On 2/5/20 12:42 PM, Marc Zyngier wrote:
> 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.

That question was more in the direction of ST, to see how it fits in
their design/plans. I would hate to work on something only to have it
rejected because ST developed something else in parallel.

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