linux-kernel - Re: [PATCH v5 1/3] dt-bindings: interrupt-controller: Add Actions SIRQ controller binding

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Message-ID: <20200827185456.GA2475396@BV030612LT>
Date:   Thu, 27 Aug 2020 21:54:56 +0300
From:   Cristian Ciocaltea <cristian.ciocaltea@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Rob Herring <robh@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Andreas Färber <afaerber@...e.de>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-actions@...ts.infradead.org
Subject: Re: [PATCH v5 1/3] dt-bindings: interrupt-controller: Add Actions
 SIRQ controller binding

On Thu, Aug 27, 2020 at 04:42:04PM +0100, Marc Zyngier wrote:
> Cristian,
> 
> On 2020-08-27 16:24, Cristian Ciocaltea wrote:
> > Hi Marc,
> > 
> > On Thu, Aug 27, 2020 at 11:35:06AM +0100, Marc Zyngier wrote:
> > > On 2020-08-27 11:06, Cristian Ciocaltea wrote:
> > > > On Wed, Aug 26, 2020 at 04:48:38PM -0600, Rob Herring wrote:
> > > > > On Wed, Aug 26, 2020 at 3:42 PM Cristian Ciocaltea
> > > > > <cristian.ciocaltea@...il.com> wrote:
> > > 
> > > [...]
> > > 
> > > > > Ultimately the GIC trigger type has to be
> > > > > something. Is it fixed or passed thru? If the latter, just use 0
> > > > > (IRQ_TYPE_NONE) if the GIC trigger mode is not fixed. Having some sort
> > > > > of translation of the trigger is pretty common.
> > > >
> > > > Yes, as explained above, the SIRQ controller performs indeed the
> > > > translation of the incoming signal. So if I understand correctly, your
> > > > suggestion would be to use the following inside the sirq node:
> > > >
> > > > interrupts = <GIC_SPI 13 IRQ_TYPE_NONE>, /* SIRQ0 */
> > > >              [...]
> > > 
> > > Please don't. If you are describing a GIC interrupt, use a
> > > trigger that actually exists. Given that you have a 1:1
> > > mapping between input and output, just encode the output
> > > trigger that matches the input.
> > 
> > Understood, the only remark here is that internally, the driver will
> > not use this information and instead will continue to rely on the input
> > to properly set the trigger type for the output.
> 
> It's fine. The binding has to be consistent on its own, but
> doesn't dictate the way the driver does thing.
> 
> > The question is if the driver should also emit a warning (or error?)
> > when the trigger type supplied via DT doesn't match the expected value.
> 
> Rob will tell you that the kernel isn't a validation tool for broken
> DTs. Shout if you want, but you are allowed to simply ignore the
> output trigger for example
> 
> > If yes, we should also clarify what the user is supposed to provide in
> > the controller node: the trigger type before the conversion (the input)
> > or the one after the conversion (the output).
> 
> The output of a SIRQ should be compatible with the GIC input it is
> attached to. You can have:
> 
>         device (LEVEL_LOW) -> SIRQ (LEVEL_HIGH) -> GIC
> 
> but you can't have:
> 
>         device (LEVEL_LOW) -> SIRQ (EDGE_RISING) -> GIC
> 
> because that's not an acceptable transformation for the SIRQ,
> nor can you have:
> 
>         device (EDGE_FALLING) -> SIRQ (EDGE_FALLING) -> GIC
> 
> because EDGE_FALLING isn't a valid input for the GIC.
> 
> In both of the invalid cases, you would be free to apply
> which ever transformation actually makes sense, and shout
> at the user if you want to help them debugging their turf.
> The later part is definitely optional.
> 
> Hope this helps,

This certainly helps a lot, now I have a clear understanding of what is
to be done next.

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

Many thanks for the detailed explanations,
Cristi