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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Dexuan Cui <decui@microsoft.com>
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Subject: Re: [PATCH] ACPI: PM: Make acpi_sleep_state_supported() non-static
Date:   Fri, 05 Jul 2019 11:40:33 +0200
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On Thursday, July 4, 2019 4:43:32 AM CEST Dexuan Cui wrote:
> 
> With some upcoming patches to save/restore the Hyper-V drivers related
> states, a Linux VM running on Hyper-V will be able to hibernate. When
> a Linux VM hibernates, unluckily we must disable the memory hot-add/remove
> and balloon up/down capabilities in the hv_balloon driver
> (drivers/hv/hv_balloon.c), because these can not really work according to
> the design of the related back-end driver on the host.
> 
> By default, Hyper-V does not enable the virtual ACPI S4 state for a VM;
> on recent Hyper-V hosts, the administrator is able to enable the virtual
> ACPI S4 state for a VM, so we hope to use the presence of the virtual ACPI
> S4 state as a hint for hv_balloon to disable the aforementioned
> capabilities. In this way, hibernation will work more reliably, from the
> user's perspective.
> 
> By marking acpi_sleep_state_supported() non-static, we'll be able to
> implement a hv_is_hibernation_supported() API in the always-built-in
> module arch/x86/hyperv/hv_init.c, and the API will be called by hv_balloon.
> 
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> ---
> 
> Previously I posted a version that tries to export the function:
> https://lkml.org/lkml/2019/6/14/1077, which may be an overkill.
> 
> So I proposed a second patch (which covers this patch and shows how this
> patch will be used): https://lkml.org/lkml/2019/6/19/861
> 
> I explained the situation in detail here: https://lkml.org/lkml/2019/6/21/63
> (a correction: old Hyper-V hosts can support guest hibernation, but some
> important functionalities in the host's management tool stack are missing).
> 
> There is no further reply in that discussion, so I'm sending this patch to
> draw people's attention again. :-)
> 
>  drivers/acpi/sleep.c    | 2 +-
>  include/acpi/acpi_bus.h | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
> index 8ff08e531443..d1ff303a857a 100644
> --- a/drivers/acpi/sleep.c
> +++ b/drivers/acpi/sleep.c
> @@ -77,7 +77,7 @@ static int acpi_sleep_prepare(u32 acpi_state)
>  	return 0;
>  }
>  
> -static bool acpi_sleep_state_supported(u8 sleep_state)
> +bool acpi_sleep_state_supported(u8 sleep_state)
>  {
>  	acpi_status status;
>  	u8 type_a, type_b;
> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> index 31b6c87d6240..3e6563e1a2c0 100644
> --- a/include/acpi/acpi_bus.h
> +++ b/include/acpi/acpi_bus.h
> @@ -651,6 +651,12 @@ static inline int acpi_pm_set_bridge_wakeup(struct device *dev, bool enable)
>  }
>  #endif
>  
> +#ifdef CONFIG_ACPI_SYSTEM_POWER_STATES_SUPPORT
> +bool acpi_sleep_state_supported(u8 sleep_state);
> +#else
> +bool acpi_sleep_state_supported(u8 sleep_state) { return false; }
> +#endif
> +
>  #ifdef CONFIG_ACPI_SLEEP
>  u32 acpi_target_system_state(void);
>  #else
> 

Applied, thanks!