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

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Message-ID: <e19b5006-c6b5-4e72-a3bf-42fa6833936a@tuxon.dev>
Date: Wed, 24 Sep 2025 18:45:13 +0300
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
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, Geert,

On 9/24/25 16:44, Geert Uytterhoeven wrote:
> 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? 

I found this issue by reading the exported regmap debug file:

cat /sys/kernel/debug/regmap/11020000.system-controller-rz_sysc_regs/registers

Thank you,
Claudiu

> 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