linux-kernel - Re: [PATCH 1/4] dt-binding: irq: imx-irqsteer: use irq number per channel instead of group number

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Message-ID: <864la0ap6k.wl-marc.zyngier@arm.com>
Date:   Tue, 22 Jan 2019 11:48:19 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Aisheng Dong <aisheng.dong@....com>
Cc:     Lucas Stach <l.stach@...gutronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        dl-linux-imx <linux-imx@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH 1/4] dt-binding: irq: imx-irqsteer: use irq number per channel instead of group number

On Tue, 22 Jan 2019 10:56:42 +0000,
Aisheng Dong <aisheng.dong@....com> wrote:
> 
> > From: Marc Zyngier [mailto:marc.zyngier@....com]
> > Sent: Friday, January 18, 2019 6:12 PM
> [...]
> > >> From: Marc Zyngier [mailto:marc.zyngier@....com]
> > >> Sent: Friday, January 18, 2019 5:39 PM On 18/01/2019 08:48, Lucas
> > >> Stach wrote:
> > >>> Am Freitag, den 18.01.2019, 07:53 +0000 schrieb Aisheng Dong:
> > >>>> Not all 64 interrupts may be used in one group. e.g. most irqsteer
> > >>>> in imx8qxp and imx8qm subsystems supports only 32 interrupts.
> > >>>>
> > >>>> As the IP integration parameters are Channel number and interrupts
> > >>>> number, let's use fsl,irqs-per-chan to represents how many
> > >>>> interrupts supported by this irqsteer channel.
> > >>>
> > >>> Sorry, but total NACK. I've got to great lengths with dumping the
> > >>> actually implemented register layout on i.MX8M and AFAICS the IRQs
> > >>> are always managed in groups of 64 IRQs, even if less than that are
> > >>> connected as input IRQs. This is what the actually present register
> > >>> set on i.MX8M tells us.
> > >>
> > >> Also, I'd really like the DT bindings not to change at every release.
> > >> So whatever change (if any) has to be done for this driver to support
> > >> existing HW, please make sure that the DT bindings are kept as stable as
> > possible.
> > >>
> > >
> > > Sorry I should clarify it a bit.
> > > There's still no users in Devicetree.
> > > So I guess we can update it, right? Or not?
> > 
> > What do you mean by no users? This driver is in 5.0, and I assume people are
> > using it one way or another. Not having a platform in the kernel tree is pretty
> > much irrelevant, as the kernel tree is not a canonical repository of existing
> > platforms.
> > 
> 
> I understand the concern.
> Theoretically yes, but it's very unlikely that there's already an out of tree users
> wants to use it for a long term as we're still at the very initial stage.
> 
> And the most important reason is that current using actually is wrong.
> We can also choose to mark it as 'depreciated' and keep the backward compatibility in driver,
> but I'm not sure whether it's worthy to do it as we may add a lot ugly code in driver
> benefits no users.
> 
> Ideas?

At this stage, and given that there is no consensus on how this driver
should work, I'm tempted to just rip it out entirely by reverting
0136afa08967 and be done with it until people work out a way forward.

	M.

-- 
Jazz is not dead, it just smell funny.