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

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Message-ID: <20251130000259.36c37b4e@kemnade.info>
Date: Sun, 30 Nov 2025 00:02:59 +0100
From: Andreas Kemnade <andreas@...nade.info>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Richard Weinberger <richard@....at>, 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>, 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

On Sat, 29 Nov 2025 16:49:11 +0100
Krzysztof Kozlowski <krzk@...nel.org> wrote:

> On 29/11/2025 16:44, Krzysztof Kozlowski wrote:
> >>         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?  
> > 
> > Fix the driver. In your case, the syscon driver.  
> 
> BTW, the state of existing TI DRA code is so poor that you don't have
> many choices... or rather every choice has drawbacks. If this was proper
> DTS, then I would say - define register map, used by regmap, for your
> compatible either in syscon driver or dedicated driver (thus new driver
> will be the syscon provider for you, just like Google GS101 syscon is
> special).
> 
> Or maybe this is not syscon at all!
> 
> Remember that syscon is a collection of miscellaneous system controller
> registers. You should not use syscon for other things, like devices with
> incomplete hardware description.
> 
It is referenced in mmu0_disp1, it looks like some syscon.
mmu0_dsp1:
...
   ti,syscon-mmuconfig = <&dsp1_system 0x0>;

So it looks valid. In code omap-iommu.c, aparrently only one register is
written.

But again, DRA7 is not my area, OMAP3-5: yes.

Regards,
Andreas