On 06/19/2017 05:24 AM, Mark Rutland wrote:

On Fri, Jun 16, 2017 at 05:07:40PM -0700, Florian Fainelli wrote:

quoted

Hi all,

Hi Florian,

quoted

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