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

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Date:   Tue, 22 Jan 2019 12:05:21 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Aisheng Dong <aisheng.dong@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "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

Am Dienstag, den 22.01.2019, 10:56 +0000 schrieb Aisheng Dong:
> > > > 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?

I'm all for doing a breaking DT change now. The binding is
significantly different from the downstream one anyways and I'm not
aware of any upstream users that wouldn't be able to cope with a change
at this point.

I want to reach a conclusion on the discussion about how the HW
actually works and is configured in reply to Patch 4/4 first.

Regards,
Lucas