linux-kernel - Re: [PATCH v3 5/7] drivers: firmware: psci: Add hierarchical domain idle states converter

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Message-ID: <6ff7c82d-4204-a339-4070-0154ab4515f1@codeaurora.org>
Date:   Wed, 5 Feb 2020 17:53:00 +0530
From:   Maulik Shah <mkshah@...eaurora.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     swboyd@...omium.org, agross@...nel.org, david.brown@...aro.org,
        Lorenzo.Pieralisi@....com, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, bjorn.andersson@...aro.org,
        evgreen@...omium.org, dianders@...omium.org, rnayak@...eaurora.org,
        ilina@...eaurora.org, lsrao@...eaurora.org, ulf.hansson@...aro.org,
        rjw@...ysocki.net
Subject: Re: [PATCH v3 5/7] drivers: firmware: psci: Add hierarchical domain
 idle states converter


On 2/4/2020 8:51 PM, Sudeep Holla wrote:
> On Tue, Feb 04, 2020 at 10:22:42AM +0530, Maulik Shah wrote:
>> On 2/3/2020 10:38 PM, Sudeep Holla wrote:
>>> On Mon, Feb 03, 2020 at 07:05:38PM +0530, Maulik Shah wrote:
>>>> From: Ulf Hansson <ulf.hansson@...aro.org>
>>>>
>>>> If the hierarchical CPU topology is used, but the OS initiated mode isn't
>>>> supported, we need to rely solely on the regular cpuidle framework to
>>>> manage the idle state selection, rather than using genpd and its
>>>> governor.
>>>>
>>>> For this reason, introduce a new PSCI DT helper function,
>>>> psci_dt_pm_domains_parse_states(), which parses and converts the
>>>> hierarchically described domain idle states from DT, into regular flattened
>>>> cpuidle states. The converted states are added to the existing cpuidle
>>>> driver's array of idle states, which make them available for cpuidle.
>>>>
>>> And what's the main motivation for this if OSI is not supported in the
>>> firmware ?
>> Hi Sudeep,
>>
>> Main motivation is to do last-man activities before the CPU cluster can
>> enter a deep idle state.
>>
> Details on those last-man activities will help the discussion. Basically
> I am wondering what they are and why they need to done in OSPM ?

Hi Sudeep,

there are cases like,

Last cpu going to deepest idle mode need to lower various resoruce 
requirements (for eg DDR freq).

This is done by calling rpmh_flush which send SLEEP values for various 
shared resources.

>>>> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
>>>> [applied to new path, resolved conflicts]
>>>> Signed-off-by: Maulik Shah <mkshah@...eaurora.org>
>>>> ---
>>>>    drivers/cpuidle/cpuidle-psci-domain.c | 137 +++++++++++++++++++++++++++++-----
>>>>    drivers/cpuidle/cpuidle-psci.c        |  41 +++++-----
>>>>    drivers/cpuidle/cpuidle-psci.h        |  11 +++
>>>>    3 files changed, 153 insertions(+), 36 deletions(-)
>>>>
>>>> diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
>>>> index 423f03b..3c417f7 100644
>>>> --- a/drivers/cpuidle/cpuidle-psci-domain.c
>>>> +++ b/drivers/cpuidle/cpuidle-psci-domain.c
>>>> @@ -26,13 +26,17 @@ struct psci_pd_provider {
>>>>    };
>>>>
>>>>    static LIST_HEAD(psci_pd_providers);
>>>> -static bool osi_mode_enabled __initdata;
>>>> +static bool osi_mode_enabled;
>>>>
>>>>    static int psci_pd_power_off(struct generic_pm_domain *pd)
>>>>    {
>>>>    	struct genpd_power_state *state = &pd->states[pd->state_idx];
>>>>    	u32 *pd_state;
>>>>
>>>> +	/* If we have failed to enable OSI mode, then abort power off. */
>>>> +	if ((psci_has_osi_support()) && !osi_mode_enabled)
>>>> +		return -EBUSY;
>>>> +
>>> Why is this needed ? IIUC we don't create genpd domains if OSI is not
>>> enabled.
>> we do create genpd domains, for cpu domains, we just abort power off here
>> since idle states are converted into regular flattened mode.
>>
> OK, IIRC the OSI patches from Ulf didn't add the genpd or rather removed
> them in case of any failure to enable OSI. Has that been changed ? If so,
> why ?
>
>> however genpd poweroff will be used by parent domain (rsc in this case)
>> which is kept in hireachy in DTSI with cluster domain to do last man
>> activities.
>>
> I am bit confused here. Either we do OSI or PC and what you are describing
> sounds like a mix-n-match to me and I am totally against it.

we still do PC based on sc7180. there is no OSI.

can you please check v4 series, i have cleaned this change by remove 
converter part.

Thanks,

Maulik

>
> --
> Regards,
> Sudeep

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