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

[Cristian Marussi <cristian.marussi@arm.com>]

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.

Hi Dhruva,

this in general mostly fine to me.

> 
> Key changes:
> - Scan device tree to identify which power domains are actually referenced
> - 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.
> 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.
> 
> Signed-off-by: Dhruva Gole <d-gole@ti.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.
> 
> This greatly helps to improve the boot time, and I have some data to
> back this up as well. This[2] experiment was done on a TI AM62L SoC
> (which is yet to make it upstream) to measure the time taken in the scmi
> pm domain probe function when it does a full 0..N scmi pd init vs just
> the ones being used in the device tree.
> 
> If you have any feedback on this, please let me know. If not, I will go
> ahead and post a "non-RFC" patch assuming everyone is mostly on board
> with this. Also request other SCMI consumers to test this out as much as
> possible to see if it breaks in any situations.

I'll post a few minor remarks on the upcoming non-RFC.

Thanks,
Cristian