linux-kernel - Re: [PATCH v2 1/2] arm64: dts: ti: k3-am65: disable optional peripherals by default

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Message-ID: <YgEBml9HvFzSl289@atomide.com>
Date:   Mon, 7 Feb 2022 13:25:14 +0200
From:   Tony Lindgren <tony@...mide.com>
To:     Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc:     Rob Herring <robh+dt@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Olof Johansson <olof@...om.net>, soc@...nel.org,
        Vignesh Raghavendra <vigneshr@...com>,
        Tero Kristo <kristo@...nel.org>, jan.kiszka@...mens.com,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Nishanth Menon <nm@...com>
Subject: Re: [PATCH v2 1/2] arm64: dts: ti: k3-am65: disable optional
 peripherals by default

* Matthias Schiffer <matthias.schiffer@...tq-group.com> [220207 08:45]:
> Generally I think that it's a bootloader's responsiblity to disable
> unneeded devices - the kernel may not even have a driver for some
> peripherals, leading to the same behaviour as a "disabled" status. For
> this reason I believe that it should always be okay to set unneeded
> devices to "disabled", and it should be considered a safe default.

Not possible, think kexec for example :) How would the previous kernel
even know what to disable if Linux has no idea about the devices?

If there are issues you're seeing, it's likely a bug in some of the
device drivers for not checking for the necessary resources like
pinctrl for i2c lines.

> I'm not sure what the consensus on these issues is. I'm more familiar
> with NXP's i.MX and Layerscape SoCs, where it's common to have all
> muxable peripherals set to "disabled" in the base DTSI, and a quick
> grep through a few dts directories gives me the impression that this is
> the case for most other vendors as well.

This approach only works for SoCs that don't need the kernel to idle
devices for runtime PM.

Regards,

Tony