linux-kernel - Re: [PATCH 2/5] dt-bindings: mfd: syscon: Add ti,am62-ddr-pmctrl

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Message-ID: <8fe546e7-4fbc-4c63-ad0f-576ffb117508@baylibre.com>
Date: Tue, 22 Apr 2025 11:12:47 -0500
From: David Lechner <dlechner@...libre.com>
To: Andrew Davis <afd@...com>,
 Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 Markus Schneider-Pargmann <msp@...libre.com>
Cc: Lee Jones <lee@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Siddharth Vadapalli <s-vadapalli@...com>,
 Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
 Tero Kristo <kristo@...nel.org>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/5] dt-bindings: mfd: syscon: Add ti,am62-ddr-pmctrl

On 4/21/25 12:03 PM, Andrew Davis wrote:

...

> Which parent device? That is my point, if the top level node for the
> whole CTRL_MMR region is made into one big syscon, then a big regmap
> is made that covers the whole region. All the child devices also make
> regmaps covering their device range. Now these registers under the child
> device belong to two different regmaps. No synchronization is done as
> these are not the same regmap, regmap only handles this for multiple
> access to registers within the same regmap.
> 

Why does the child device have to create a new/separate regmap? Can it not use
something like syscon_regmap_lookup_by_phandle_args() to get the regmap from
the "syscon" node along with 1 or more args specifying the one or few registers
out of the full range that are assigned to that specific child node? This way,
all child nodes would be using the same shared regmap.

(And yes, I know technically they don't need to be child nodes - just using that
terminology to be consistent with the previous discussion.)