Re: [Linux-stm32] [PATCH] firmware: psci: handle unsupported SET_SUSPEND_MODE in PC mode

[Patrick DELAUNAY <patrick.delaunay@foss.st.com>]

Hi,

On 10/30/26 11:04, Patrick DELAUNAY wrote:
> Hi,
>
> On 10/30/26 09:32, Sudeep Holla wrote:
>> On Thu, Oct 29, 2026 at 07:16:25PM +0100, Patrick Delaunay wrote:
>>> The PSCI specification makes PSCI_SET_SUSPEND_MODE optional. If it
>>> returns NOT_SUPPORTED when Linux requests platform-coordinated (PC)
>>> mode, Linux can assume that PC mode is in effect. Treat this response
>>> as success so PSCI power-domain providers can initialize when firmware
>>> does not support OS-initiated (OSI) mode.
>>>
>>> Continue to report an error when OSI mode is requested but
>>> SET_SUSPEND_MODE is not supported.
>>>
>> So, your platform advertises the presence/support for OSI mode and yet
>> opted for not implementing SET_SUSPEND_MODE ? If so, it is indeed a
>> firmware bug as reported.
>>
>
> I think it is no realy a platform bug but a too strict management in 
> Linux kernel,
>
> for PSCI power domain.
>
>
> The OSI mode is not yet supported by the STM32MP25 platform in Linux at
>
> upstream but I introduce PSCI domains in device tree (but without idle 
> power
>
> domain) just to prepare this activation in next steps.
>
>
> As the PSCI support is not activated in Firmware (TF-A BL31), the 
> firmware correctly
>
> expose its capacities (PSCI_OS_INIT_MODE =0)
>
> => PSCI feature indicate that OSI is not supported 
> (FF_SUPPORTS_OS_INIT_MODE = 0)
>
> => PSCI_SET_SUSPEND_MODE function is not supported (optional when OSI 
> is not supported)
>
>
> in Linux side, the power domain driver 
> (drivers/cpuidle/cpuidle-psci-domain.c)
>
> correctly check the support of OSI:
>
>     bool use_osi = psci_has_osi_support();
>
>
> in STM32MP25 platform use_osi = false, so the driver request
>
> Plafrom Cooordinated mode (PC mode) as expected
>
> But here  the GENPD driver try to use optional function to set mode:
>
>
>     /* let's try to enable OSI. */
>     ret = psci_set_osi_mode(use_osi);
>     if (ret)
>         goto remove_pd;
>
>
> And the problem occurs here because the optional function is called 
> but the normal use case
>
> is not handled (OSI mode not supported / PSCI_SET_SUSPEND_MODE not 
> supported)
>
>
> With the proposed patch, the Linux kernel can have PSCI domain in 
> device tree even when
>
> PSCI OSI support is deactivated in PSCI firmware (or not yet 
> activated): the domain are
>
> always ON (GENPD_FLAG_ALWAYS_ON)
>
>
> NB: I hesitate between the current patch and a patch in PSCI power 
> domain driver:
>
>
>     /* let's try to enable OSI. */
>     ret = psci_set_osi_mode(use_osi);
>
> + if (ret == -EOPNOTSUPP && !use_osi)
>
> +    ret = 0;
>
>     if (ret)
>         goto remove_pd;
>
>
> but I patch PSCI firmware driver because I think it is a more generic 
> place to handle optional PSCI function.
>
>
> Regards
>
>
> Patrick


To complete my previous answer,

In  last PSCI specification v1.3, we found this description:

"

5.21 PSCI_SET_SUSPEND_MODE

5.21.3 Caller responsibilities

The caller must be able to cope with the following error return codes:
• NOT_SUPPORTED, in which case the calling OS can assume the platform 
will work in platform-
coordinated mode. In this case, the PSCI_FEATURES feature flag 0 for 
CPU_SUSPEND is also 0.

"


My patch only implements this behavior:

the PSCI stack in Linux assumes PC mode when SET_SUSPEND_MODE is not 
supported.


Regards

Patrick