[PATCH] arm64: Kconfig: select PM for ARCH_VEXPRESS

[Arnd Bergmann]

On Thursday, June 16, 2016 4:15:28 PM CEST Sudeep Holla wrote:
> The Linux AMBA bus framework probes the peripheral IDs when adding the
> AMBA devices very early on the boot. Generally they are on APB bus and
> just require APB clocks to be on even when most of the core logic of the
> IP is powered down.
> 
> However on Juno, the entire debugsys domain needs to be ON to access
> even the coresight components' CID/PID registers and hence broken by
> design. Accessing those while debugsys power domain is off will lead to
> the bridge stalling the transactions instead of returning the slave error.
> 
> Further, the AMBA framework can't deal with !CONFIG_PM case: it ignores
> the error and proceeds to access the device region. It was suggested to
> always enable CONFIG_PM in order to handle this scenario.
> 
> Suggested-by: Ulf Hansson <ulf.hansson at linaro.org>
> Signed-off-by: Sudeep Holla <sudeep.holla at arm.com>
> ---
>  arch/arm64/Kconfig.platforms | 1 +
>  1 file changed, 1 insertion(+)
> 
> Hi ARM-SoC team,
> 
> The discussion on this happened on linux-pm list[1]. This is need on
> Juno once we introduce coresight components in the DT. With !CONFIG_PM,
> the board stalls on boot and hence this patch is needed. This shouldn't
> change any thing in the defconfig as couple of other platforms already
> do the same. It's needed in case all other ARCH_* configs are disabled.
> 
> Without this, we need a dirty trick in the DT[2] to handle !CONFIG_PM.
> 
> Can you please pick this for v4.8 ?

Question: if AMBA cannot deal with CONFIG_PM disabled, should 
the 'select' be done from CONFIG_ARM_AMBA instead?

I also feel a little uncomfortable with just adding 'select PM', given
that this option is normally just implied by CONFIG_SUSPEND ||
CONFIG_HIBERNATE_CALLBACKS, but not selected individually, so we
might run into regressions when we get configurations that were
invalid before. Then again ARCH_RENESAS seems to already do this.

	Arnd