linux-kernel - Re: [PATCH] soc: renesas: rz-sysc: Populate readable_reg/writeable

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Message-ID: <CAMuHMdXKbPGqAnAcL2kFyF6K3hH9=gr8ECAFVpkgj-OL1mB4eg@mail.gmail.com>
Date: Wed, 24 Sep 2025 15:44:05 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Claudiu <claudiu.beznea@...on.dev>
Cc: magnus.damm@...il.com, john.madieu.xa@...renesas.com, 
	linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH] soc: renesas: rz-sysc: Populate readable_reg/writeable_reg
 in regmap config

Hi Claudiu,

On Mon, 22 Sept 2025 at 09:41, Claudiu <claudiu.beznea@...on.dev> wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>
> Not all system controller registers are accessible from Linux. Accessing
> such registers generates synchronous external abort. Populate the
> readable_reg and writeable_reg members of the regmap config to inform the
> regmap core which registers can be accessed. The list will need to be
> updated whenever new system controller functionality is exported through
> regmap.
>
> Fixes: 2da2740fb9c8 ("soc: renesas: rz-sysc: Add syscon/regmap support")
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>

Thanks for your patch!

How can this be triggered? AFAIU, registers are only accessed as
obtained from syscon_regmap_lookup_by_phandle_args(), i.e. based on the
register offset stored in the DTB.  If the offset in the DTB is wrong,
there is not much we can do ("garbage in, garbage out"), and the DTB
should be fixed instead.

Is there another way the user can access these non-existing registers?
Thanks!

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds