linux-kernel - RE: [PATCH] gpio: dwapb: Add support for 32 interrupts

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Date:   Fri, 6 Apr 2018 10:20:46 +0000
From:   Phil Edworthy <phil.edworthy@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Hoan Tran <hotran@....com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Michel Pollet <michel.pollet@...renesas.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] gpio: dwapb: Add support for 32 interrupts

Hi Geert,

On 06 April 2018 10:57 Geert Uytterhoeven wrote:
> On Thu, Apr 5, 2018 at 11:42 AM, Phil Edworthy wrote:
> > On 30 March 2018 22:26 Andy Shevchenko wrote:
> >> On Wed, Mar 28, 2018 at 5:22 PM, Phil Edworthy wrote:
> >> > The DesignWare GPIO IP can be configured for either 1 or 32
> >> > interrupts,
> >>
> >> 1 to 32, or just a choice between two?
> > Just a choice of 1 or 32.
> > Note that by 'configured' I am talking about the hardware being
> > configured in RTL prior to manufacturing a device. Once made, you cannot
> change it.
> > This configuration affects the number of output interrupt signals from
> > the GPIO Controller block that are connected to an interrupt controller.
> 
> Differentiating between different versions of an IP block using DT properties
> is usually a bad idea, for several reasons:
>   - What if you discover another difference later?
>   - You cannot add differentiating properties retroactively, because of
> backwards
>      compatibility with old DTBS.
> 
> Hence I think you should introduce a new compatible value instead.

This is not a different version of the IP, just a different configuration option.
Most IP blocks have a huge number of knobs that can be twiddled by the HW
people, such as cache size, UART fifo depth. I think this is no different.

Thanks
Phil