linux-kernel - RE: [PATCH v3 09/10] arch: arm: boot: dts: Introduce HPE GXP Device tree

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Date:   Fri, 1 Apr 2022 16:05:25 +0000
From:   "Hawkins, Nick" <nick.hawkins@....com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     "Verdun, Jean-Marie" <verdun@....com>,
        Olof Johansson <olof@...om.net>,
        "soc@...nel.org" <soc@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 09/10] arch: arm: boot: dts: Introduce HPE GXP Device
 tree



-----Original Message-----
From: Arnd Bergmann [mailto:arnd@...db.de] 
Sent: Thursday, March 31, 2022 4:53 PM
To: Hawkins, Nick <nick.hawkins@....com>
Cc: Arnd Bergmann <arnd@...db.de>; Verdun, Jean-Marie <verdun@....com>; Olof Johansson <olof@...om.net>; soc@...nel.org; Rob Herring <robh+dt@...nel.org>; linux-arm-kernel@...ts.infradead.org; devicetree@...r.kernel.org; linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 09/10] arch: arm: boot: dts: Introduce HPE GXP Device tree


> I don't think you can do this, if you are using the syscon regmap, you go through the regmap indirection rather than accessing the mmio register by virtual address, and this may result in some extra code in your driver, and a little runtime overhead.

> If you prefer to avoid that, you can go back to having the timer node as the parent, but without being a syscon. In this case, the watchdog would be handled in one of these ways:

> a) a child device gets created from the clocksource driver and bound to the
    watchdog driver, which then uses a private interface between the clocksource
    and the watchdog to access the registers

> b) the clocksource driver itself registers as a watchdog driver, without
    having a separate driver module

> One thing to consider is whether the register range here contains any registers that may be used in another driver, e.g. a second timer, a PWM, or a clk controller. If not, you are fairly free to pick any of these approaches.

I will try to use the b) approach everything in that range is timer or watchdog related. There is a second timer however there are no plans on using that. Should the combined code still live inside the driver/timer directory or should it be moved to mfd?

Thanks,

-Nick