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

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Message-ID: <b89cf979-b2b2-4534-a633-648dc640e3ad@kernel.org>
Date: Mon, 1 Dec 2025 22:41:45 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Richard Weinberger <richard@....at>
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

On 01/12/2025 22:34, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
>> Von: "Krzysztof Kozlowski" <krzk@...nel.org>
>>>>> 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.
>>>
>>> Please help me to understand what the desired behavior of the driver is.
>>>
>>> Currently syscon creates one regmap for everything and passes this regmap
>>> to the individual syscon users.
>>> These users have to know what offset within the regmap is their playground.
>>> If I understand correctly, it would be better if every syscon user would
>>> register their own regmap?
>>
>> I don't think so. This device driver, so the syscon, creates the regmap
>> and knows EXACTLY which registers are valid or not. It is not
>> responsibility of the consumer to tell the syscon what this syscon is.
>> Syscon knows that...
> 
> How to configure this in syscon?
> AFAIK it takes only a single reg property.
> Are you suggesting to add many more syscon nodes to the DT to skip the holes?
> 
> Currently the scm_conf@0 DT node defines the first 0x1400 bytes
> of the CTRL_MODULE_CORE register[0].
> 
> Reading from register 0x180 triggers an async data abort here.
> The manual describes it as "RESERVED" of type "R".
> Lots of other offsets in CTRL_MODULE_CORE are reserved, but reading works.
> 
> Long story short, please tell me how to model it in DT and I'll do so.

I already told you:

"...we had it in several devices and fixed drivers."

"Fix the driver. In your case, the syscon driver."

and finally:

"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)."

What to say more? This is the instruction/proposal.

Best regards,
Krzysztof