Subject: Re: [PATCH v4 10/14] cpuidle: psci: Prepare to use OS initiated suspend mode via PM domains

From: Sudeep Holla <[email-masked]>
Date: Thu, 19 Dec 2019 14:31:54 +0000

On Wed, Dec 11, 2019 at 04:43:39PM +0100, Ulf Hansson wrote:
> The per CPU variable psci_power_state, contains an array of fixed values,
> which reflects the corresponding arm,psci-suspend-param parsed from DT, for
> each of the available CPU idle states.
>
> This isn't sufficient when using the hierarchical CPU topology in DT, in
> combination with having PSCI OS initiated (OSI) mode enabled. More
> precisely, in OSI mode, Linux is responsible of telling the PSCI FW what
> idle state the cluster (a group of CPUs) should enter, while in PSCI
> Platform Coordinated (PC) mode, each CPU independently votes for an idle
> state of the cluster.
>
> For this reason, introduce a per CPU variable called domain_state and
> implement two helper functions to read/write its value. Then let the
> domain_state take precedence over the regular selected state, when entering
> and idle state.
>
> To avoid executing the above OSI specific code in the ->enter() callback,
> while operating in the default PSCI Platform Coordinated mode, let's also
> add a new enter-function and use it for OSI.
>
> Co-developed-by: Lina Iyer <[email-masked]>
> Signed-off-by: Lina Iyer <[email-masked]>
> Signed-off-by: Ulf Hansson <[email-masked]>
> ---
>
> Changes in v4:
> 	- Rebased on top of earlier changes.
> 	- Add comment about using the deepest cpuidle state for the domain state
> 	selection.
>
> ---
>  drivers/cpuidle/cpuidle-psci.c | 56 ++++++++++++++++++++++++++++++----
>  1 file changed, 50 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
> index 6a87848be3c3..9600fe674a89 100644
> --- a/drivers/cpuidle/cpuidle-psci.c
> +++ b/drivers/cpuidle/cpuidle-psci.c
> @@ -29,14 +29,47 @@ struct psci_cpuidle_data {
>  };
>
>  static DEFINE_PER_CPU_READ_MOSTLY(struct psci_cpuidle_data, psci_cpuidle_data);
> +static DEFINE_PER_CPU(u32, domain_state);
> +

[...]

> +static int psci_enter_domain_idle_state(struct cpuidle_device *dev,
> +					struct cpuidle_driver *drv, int idx)
> +{
> +	struct psci_cpuidle_data *data = this_cpu_ptr(&psci_cpuidle_data);
> +	u32 *states = data->psci_states;

Why can't the above be like this for consistency(see below in
psci_enter_idle_state) ?

 	u32 *states = __this_cpu_read(psci_cpuidle_data.psci_states);

> +	u32 state = psci_get_domain_state();
> +	int ret;
> +
> +	if (!state)
> +		state = states[idx];
> +
> +	ret = psci_enter_state(idx, state);
> +
> +	/* Clear the domain state to start fresh when back from idle. */
> +	psci_set_domain_state(0);
> +	return ret;
> +}
>

[...]

> @@ -118,6 +152,15 @@ static int __init psci_dt_cpu_init_idle(struct device_node *cpu_node,
>  			ret = PTR_ERR(data->dev);
>  			goto free_mem;
>  		}
> +
> +		/*
> +		 * Using the deepest state for the CPU to trigger a potential
> +		 * selection of a shared state for the domain, assumes the
> +		 * domain states are all deeper states.
> +		 */
> +		if (data->dev)

You can drop this check as return on error above.

> +			drv->states[state_count - 1].enter =
> +				psci_enter_domain_idle_state;

I see the comment above but this potential blocks retention mode at
cluster level when all cpu enter retention at CPU level. I don't like
this assumption, but I don't have any better suggestion. Please add the
note that we can't enter RETENTION state at cluster/domain level when
all CPUs enter at CPU level.

As I wrote above I got another doubt. What if platform specifies just
RETENTION state at CPU as well as Cluster/domain ? I think it should be
fine, just asking it out loud.

--
Regards,
Sudeep

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