linux-kernel - Re: [RFC PATCH] pmdomain: arm: scmi_pm_domain: Do lazy init as part of probe

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Message-ID: <20250530-honest-chital-of-growth-db31e1@sudeepholla>
Date: Fri, 30 May 2025 17:31:08 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: Dhruva Gole <d-gole@...com>
Cc: Cristian Marussi <cristian.marussi@....com>,
	Sudeep Holla <sudeep.holla@....com>,
	Ulf Hansson <ulf.hansson@...aro.org>, arm-scmi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] pmdomain: arm: scmi_pm_domain: Do lazy init as part
 of probe

On Fri, May 30, 2025 at 04:05:27PM +0530, Dhruva Gole wrote:
> Optimize the SCMI power domain driver to only initialize domains that are
> actually referenced in the device tree. Previously, the driver would
> initialize all possible domains up to the maximum ID, which could lead to
> unnecessary firmware calls and longer probe times.
> 
> Key changes:
> - Scan device tree to identify which power domains are actually referenced

How do this work with runtime DT overlays ?

> - Use bitmap to track needed domains instead of initializing all
> - Only perform state queries and initialization for referenced domains
> - Maintain proper array sizing for power domain framework compatibility
> - Keep full provider structure to support late binding
> 
> This optimization reduces probe time and unnecessary firmware interactions
> by only initializing power domains that are actually used in the system.

Why is this very specific to power domains only ? This must apply for other
domains like perf or clock or reset ?

> For example, in a system with 100 possible domains but only 3 referenced
> in the device tree, we now only initialize those 3 domains instead of
> all 100.
> 

Well, how much of these PD will get used in the final products ? I can
understand the need to use just 3 in devel platforms. Just trying to see
how realistic is the scenario ? Is there any other optimisation possible
from the firmware ? Does getting the state of a PD takes so much time
on the platform in question ?

> Signed-off-by: Dhruva Gole <d-gole@...com>
> ---
> 
> Hi all,
> The approach of doing a lazy init was briefly proposed in this [1] 2024
> Embedded Open Source talk. It was also brought up in the monthly ARM
> SCMI meetings that take place and it didn't recieve too much opposition.
> 

Sorry, I must have missed that one.

-- 
Regards,
Sudeep