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

[AngeloGioacchino Del Regno]

Il 04/02/26 09:54, Tzung-Bi Shih ha scritto:
> 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.
> 
> Fixes: d935187cfb27 ("remoteproc: mediatek: Break lock dependency to prepare_lock")
> Signed-off-by: Tzung-Bi Shih <tzungbi at kernel.org>

Would be great if you could mention that in this driver, at the moment of writing,
there is no .attach() callback, hence rproc->state can never be RPROC_ATTACHED (as
in case that would also leave the clock prepared).

In any case, even though I don't exactly *love* how this is actually done, I don't
really have any better option.

But....

> ---
>   drivers/remoteproc/mtk_scp.c | 28 ++++++++++++++++++++++++++++
>   1 file changed, 28 insertions(+)
> 
> diff --git a/drivers/remoteproc/mtk_scp.c b/drivers/remoteproc/mtk_scp.c
> index 4651311aeb07..6200c687e232 100644
> --- a/drivers/remoteproc/mtk_scp.c
> +++ b/drivers/remoteproc/mtk_scp.c
> @@ -1592,12 +1592,40 @@ static const struct of_device_id mtk_scp_of_match[] = {
>   };
>   MODULE_DEVICE_TABLE(of, mtk_scp_of_match);
>   
> +#ifdef CONFIG_PM_SLEEP

...you don't need this ifdef as when CONFIG_PM_SLEEP is not set the macro
SET_SYSTEM_SLEEP_PM_OPS is stubbed out (check pm.h).

After removing the ifdef, there'll be something to change, specifically:

> +static int scp_suspend(struct device *dev)

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 */
> +	if (rproc->state == RPROC_RUNNING)
> +		clk_unprepare(scp->clk);
> +	return 0;
> +}
> +
> +static int scp_resume(struct device *dev)

static int __maybe_unused scp_resume(struct device *dev)
{

After which,

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>

Cheers,
Angelo

> +{
> +	struct mtk_scp *scp = dev_get_drvdata(dev);
> +	struct rproc *rproc = scp->rproc;
> +
> +	if (rproc->state == RPROC_RUNNING)
> +		return clk_prepare(scp->clk);
> +	return 0;
> +}
> +#endif
> +
> +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,
>   	},
>   };
>