linux-kernel - Re: [PATCH 1/4] of: Add of_parse_phandle_with_opt

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Message-ID: <560BA6AB.3060500@arm.com>
Date:	Wed, 30 Sep 2015 10:08:59 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Rob Herring <robh@...nel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <mark.rutland@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 1/4] of: Add of_parse_phandle_with_opt_args() helper function

On 29/09/15 18:28, Rob Herring wrote:
> On Tue, Sep 22, 2015 at 12:52 PM, Marc Zyngier <marc.zyngier@....com> wrote:
>> of_parse_phandle_with_args() is slightly inflexible as it doesn't
>> allow the (unusual) case where the #*-cells property is not defined.
>> In order to support this, introduce of_parse_phandle_with_opt_args()
>> which assumes that #*-cells is zero when it is not defined,
> 
> zero or cell_count - 1?

Zero is how the lack of #msi-cells property is interpreted. (cell_count
- 1) is how this is implemented.

> I would be okay with always assuming zero rather than being an error
> if that simplifies things. It is not really the kernel's job to be a
> dtb validator.

I'd be fine with that too. I'd just like it to be a defined behaviour,
not an unexpected side effect.

> Also, I assume this was done for some compatibility? In general, we
> should be explicit, so "#msi-cells = <0>" should be recommended and we
> should update dts files if they are not.

I agree that over time, we should update the existing DTS. But I hear
Mark chanting "Stable DT" behind me, so I'm inclined to provide an
transition path... ;-)

I'll respin the series later today.

Thanks,

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