linux-kernel - Re: [RFC] irqchip: add support for LS1021A external interrupt lines

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Message-ID: <2302267.dSSx8ic0iv@ws-stein>
Date:   Mon, 11 Dec 2017 15:38:13 +0100
From:   Alexander Stein <alexander.stein@...tec-electronic.com>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [RFC] irqchip: add support for LS1021A external interrupt lines

On Monday, December 11, 2017, 3:06:52 PM CET Rasmus Villemoes wrote:
> On 2017-12-11 14:45, Rasmus Villemoes wrote:
> > On 2017-12-11 11:02, Alexander Stein wrote:
> > 
> >> Oh, and what is the content of register SCFG_SCFGREVCR?
> > 
> > Good point. On my board it's 0xffffffff, set even before U-boot starts,
> > and lots board support code in U-boot expects this. I can't immediately
> > find examples in the linux source code that actually writes to the scfg,
> 
> Not a write, but we do already implicitly assume SCFG_SCFGREVCR is set
> to all-ones: In drivers/pci/dwc/pci-layerscape.c, bits which are
> numbered 6-11 in the reference manual are extracted with a regmap_read()
> followed by a left-shift by 20 and mask with 0x3f. That's consistent
> with me setting bit 0 (reference manual enumeration) using 1U<<31.

We set SCFG_SCFGREVCR to all-ones too, even before u-boot in rcw. Problem
is, this bit-reversal is only valid for SCFG. It's a shame, but at least add
a comment in the code you expect SCFG_SCFGREVCR as 0xffffffff.

Best regards,
Alexander