linux-kernel - Re: [PATCH 1/4] dt-bindings: Document new common property: has-inaccessible-regs

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Message-ID: <771947541.4509.1764430418744.JavaMail.zimbra@nod.at>
Date: Sat, 29 Nov 2025 16:33:38 +0100 (CET)
From: Richard Weinberger <richard@....at>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: linux-kernel <linux-kernel@...r.kernel.org>, 
	linux-omap <linux-omap@...r.kernel.org>, 
	devicetree <devicetree@...r.kernel.org>, 
	Arnd Bergmann <arnd@...db.de>, Lee Jones <lee@...nel.org>, 
	dakr <dakr@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Mark Brown <broonie@...nel.org>, tony <tony@...mide.com>, 
	rogerq <rogerq@...nel.org>, khilman <khilman@...libre.com>, 
	Andreas Kemnade <andreas@...nade.info>, 
	aaro koskinen <aaro.koskinen@....fi>, 
	Conor Dooley <conor+dt@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, robh <robh@...nel.org>
Subject: Re: [PATCH 1/4] dt-bindings: Document new common property:
 has-inaccessible-regs

----- Ursprüngliche Mail -----
> Von: "Krzysztof Kozlowski" <krzk@...nel.org>
> On 29/11/2025 15:20, Richard Weinberger wrote:
>> This property is used to denote that a certain register map contains
>> registers that are inaccessible under conditions only a device driver
>> can know.
> 
> So device driver controls fully their exposure via sysfs.
> 
> Binding cannot help here at all.

The driver does not expose them via sysfs, it's the regmap framework via debugfs.
 
>> The purpose of this property is to disable register access through debug
>> facilities outside of the device driver.
> 
> You described OS policy which is not suitable for bindings at all. Plus
> commit msg really mixes up two separate points - buggy driver which
> fails to properly set regmap (or other facility) with some DT-based
> restrictions.

I kind of expected this answer. ;-)

Currently arch/arm/boot/dts/ti/omap/dra7-l4.dtsi binds CTRL_MODULE_CORE to the syscon mfd driver
and various child nodes bind to subranges.
e.g.
scm_conf: scm_conf@0 {
        compatible = "syscon", "simple-bus";
        reg = <0x0 0x1400>;
        #address-cells = <1>;
        #size-cells = <1>;
        ranges = <0 0x0 0x1400>;
        has-inaccessible-regs;

        pbias_regulator: pbias_regulator@e00 {
                compatible = "ti,pbias-dra7", "ti,pbias-omap";
                reg = <0xe00 0x4>;
                syscon = <&scm_conf>;
                pbias_mmc_reg: pbias_mmc_omap5 {
                        regulator-name = "pbias_mmc_omap5";
                        regulator-min-microvolt = <1800000>;
                        regulator-max-microvolt = <3300000>;
                };      
        };      

        phy_gmii_sel: phy-gmii-sel@554 {
                compatible = "ti,dra7xx-phy-gmii-sel";
                reg = <0x554 0x4>;
                #phy-cells = <1>;
        };      

        scm_conf_clocks: clocks {
                #address-cells = <1>;
                #size-cells = <0>;
        };      
};

So, drivers like ti,pbias-dra7 or ti,dra7xx-phy-gmii-sel touch only registers
they know about and this works well.
But syscon manages the whole register map via regmap, and regmap exposes it all
via debugfs.

What solution do you propose?
Splitting reg = <0x0 0x1400> into many tiny fractions and not using an mfd anymore?

Thanks,
//richard