linux-kernel - Re: [RFC PATCH 3/3] decompress/keepalive.h: add config option for toggling a set of bits

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Message-ID: <CACRpkdYpnX0JMT9tG8AYhRQiXo90GJoF_J8c6f+KoWKvZmyj-g@mail.gmail.com>
Date:   Thu, 24 Oct 2019 14:17:15 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Gao Xiang <xiang@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Sascha Hauer <kernel@...gutronix.de>
Subject: Re: [RFC PATCH 3/3] decompress/keepalive.h: add config option for
 toggling a set of bits

On Thu, Oct 17, 2019 at 1:49 PM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:

> +config DECOMPRESS_KEEPALIVE_TOGGLE_REG
> +       hex "Address of register to modify while decompressing"
> +       help
> +         Set this to a physical address of a 32-bit memory word to
> +         modify while decompressing.
> +
> +config DECOMPRESS_KEEPALIVE_TOGGLE_MASK
> +       hex "Bit mask to toggle while decompressing"
> +       help
> +         The register selected above will periodically be xor'ed with
> +         this value during decompression.

I would not allow users to store these vital hex values in their
defconfig and other unsafe places. Instead follow the pattern from
arch/arm/Kconfig.debug for storing the DEBUG_UART_PHYS:

config DEBUG_UART_PHYS
        hex "Physical base address of debug UART"
        default 0x01c20000 if DEBUG_DAVINCI_DMx_UART0
        default 0x01c28000 if DEBUG_SUNXI_UART0
        default 0x01c28400 if DEBUG_SUNXI_UART1
....
i.e. make sure to provide the right default values. We probably
need at least one example for others to follow.

Maybe this is your plan, I don't know, wanted to point it out
anyways.

Yours,
Linus Walleij