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Re: [PATCH v3 0/4] Generalize fncpy availability

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On 06/19/2017 05:24 AM, Mark Rutland wrote:
> On Fri, Jun 16, 2017 at 05:07:40PM -0700, Florian Fainelli wrote:
>> Hi all,
> 
> Hi Florian,
> 
>> This patch series makes ARM's fncpy() implementation more generic (dropping the
>> Thumb-specifics) and available in an asm-generic header file.
>>
>> Tested on a Broadcom ARM64 STB platform with code that is written to SRAM.
>>
>> Changes in v3 (thanks Doug!):
>> - correct include guard names in asm-generic/fncpy.h to __ASM_FNCPY_H
>> - utilize Kbuild to provide the fncpy.h header on ARM64
>>
>> Changes in v2:
>> - leave the ARM implementation where it is
>> - make the generic truly generic (no)
>>
>> This is helpful in making SoC-specific power management code become true drivers
>> that can be shared between different architectures.
> > Could you elaborate on what this is needed for?

Several uses cases come to mind:

- it could be used as a trampoline code prior to entering S2 for systems
that do not support PSCI 1.0

- any code that has a specific need to relocate a performance, security
sensitive code into SRAM and use it as another pool of memory.

> 
> My understanding was that on 32-bit, this was to handle idle / suspend
> cases, whereas for arm64 that should be handled by PSCI.

For systems that support PSCI 1.0, I agree, but it may not be possible
to update those systems easily, still use case 2 is completely valid.

> 
> what exactly do you intend to use this for?

At the moment we use it to enter S2 on ARM64 systems (ARCH_BRCMSTB)
which are PSCI 0.2 only. And yes, we do have a plan to evaluate
upgrading to PSCI 1.0, but in general, any SoC which as an addressable
SRAM could use it for whatever purpose it sees fit.
-- 
Florian

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[PATCH v3 0/4] Generalize fncpy availability Florian Fainelli <f.fainelli@gmail.com> - 2017-06-17 02:10 +0200
  Re: [PATCH v3 0/4] Generalize fncpy availability Mark Rutland <mark.rutland@arm.com> - 2017-06-19 14:30 +0200
    Re: [PATCH v3 0/4] Generalize fncpy availability Tony Lindgren <tony@atomide.com> - 2017-06-19 16:00 +0200
    Re: [PATCH v3 0/4] Generalize fncpy availability Florian Fainelli <florian.fainelli@broadcom.com> - 2017-06-19 19:40 +0200
      Re: [PATCH v3 0/4] Generalize fncpy availability Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> - 2017-06-20 11:10 +0200
        Re: [PATCH v3 0/4] Generalize fncpy availability Florian Fainelli <f.fainelli@gmail.com> - 2017-06-20 18:30 +0200
          Re: [PATCH v3 0/4] Generalize fncpy availability Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> - 2017-06-20 18:50 +0200
          Re: [PATCH v3 0/4] Generalize fncpy availability Sudeep Holla <sudeep.holla@arm.com> - 2017-06-20 19:00 +0200
            Re: [PATCH v3 0/4] Generalize fncpy availability Florian Fainelli <f.fainelli@gmail.com> - 2017-06-20 19:10 +0200
  Re: [PATCH v3 0/4] Generalize fncpy availability David Howells <dhowells@redhat.com> - 2017-06-19 15:40 +0200

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