Re: [PATCH v2] remoteproc: mediatek: Unprepare SCP clock during system suspend

[Tzung-Bi Shih <tzungbi@kernel.org>]

On Fri, Feb 06, 2026 at 03:30:33AM +0000, Tzung-Bi Shih wrote:
> Prior to commit d935187cfb27 ("remoteproc: mediatek: Break lock
> dependency to prepare_lock"), `scp->clk` was prepared and enabled only
> when it needs to communicate with the SCP.  The commit d935187cfb27
> moved the prepare operation to remoteproc's prepare(), keeping the clock
> prepared as long as the SCP is running.
> 
> The power consumption due to the prolonged clock preparation can be
> negligible when the system is running, as SCP is designed to be a very
> power efficient processor.
> 
> However, the clock remains prepared even when the system enters system
> suspend.  This prevents the underlying clock controller (and potentially
> the parent PLLs) from shutting down, which increases power consumption
> and may block the system from entering deep sleep states.
> 
> Add suspend and resume callbacks.  Unprepare the clock in suspend() if
> it was active and re-prepare it in resume() to ensure the clock is
> properly disabled during system suspend, while maintaining the "always
> prepared" semantics while the system is active.  The driver doesn't
> implement .attach() callback, hence it only checks for RPROC_RUNNING.
> 
> Fixes: d935187cfb27 ("remoteproc: mediatek: Break lock dependency to prepare_lock")
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
> ---

Pardon me for forgetting to attach changelog before sending the patch.  Here
is the changelog:

v2:
- Add note and code comment for RPROC_ATTACHED.
- Use __maybe_unused instead of '#ifdef CONFIG_PM_SLEEP'.
- Add R-b tag.

v1: https://lore.kernel.org/all/20260204085442.1822123-1-tzungbi@kernel.org

>  drivers/remoteproc/mtk_scp.c | 39 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/drivers/remoteproc/mtk_scp.c b/drivers/remoteproc/mtk_scp.c
> index 4651311aeb07..bb6f6a16d895 100644
> --- a/drivers/remoteproc/mtk_scp.c
> +++ b/drivers/remoteproc/mtk_scp.c
> @@ -1592,12 +1592,51 @@ static const struct of_device_id mtk_scp_of_match[] = {
>  };
>  MODULE_DEVICE_TABLE(of, mtk_scp_of_match);
>  
> +static int __maybe_unused scp_suspend(struct device *dev)
> +{
> +	struct mtk_scp *scp = dev_get_drvdata(dev);
> +	struct rproc *rproc = scp->rproc;
> +
> +	/*
> +	 * Only unprepare if the SCP is running and holding the clock.
> +	 *
> +	 * Note: `scp_ops` doesn't implement .attach() callback, hence
> +	 * `rproc->state` can never be RPROC_ATTACHED.  Otherwise, it
> +	 * should also be checked here.
> +	 */
> +	if (rproc->state == RPROC_RUNNING)
> +		clk_unprepare(scp->clk);
> +	return 0;
> +}
> +
> +static int __maybe_unused scp_resume(struct device *dev)
> +{
> +	struct mtk_scp *scp = dev_get_drvdata(dev);
> +	struct rproc *rproc = scp->rproc;
> +
> +	/*
> +	 * Only prepare if the SCP was running and holding the clock.
> +	 *
> +	 * Note: `scp_ops` doesn't implement .attach() callback, hence
> +	 * `rproc->state` can never be RPROC_ATTACHED.  Otherwise, it
> +	 * should also be checked here.
> +	 */
> +	if (rproc->state == RPROC_RUNNING)
> +		return clk_prepare(scp->clk);
> +	return 0;
> +}
> +
> +static const struct dev_pm_ops scp_pm_ops = {
> +	SET_SYSTEM_SLEEP_PM_OPS(scp_suspend, scp_resume)
> +};
> +
>  static struct platform_driver mtk_scp_driver = {
>  	.probe = scp_probe,
>  	.remove = scp_remove,
>  	.driver = {
>  		.name = "mtk-scp",
>  		.of_match_table = mtk_scp_of_match,
> +		.pm = &scp_pm_ops,
>  	},
>  };
>  
> -- 
> 2.53.0.rc2.204.g2597b5adb4-goog
>