[PATCH v2] arm64: Kconfig: select PM{, _GENERIC_DOMAINS} for ARCH_VEXPRESS

[Sudeep Holla]

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_GENERIC_DOMAINS
case: it ignores the error and proceeds to access the device region.
It was suggested to always enable CONFIG_PM{,_GENERIC_DOMAINS} in order
to handle above explained scenario.

Cc: Arnd Bergmann <arnd at arndb.de>
Suggested-by: Ulf Hansson <ulf.hansson at linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla at arm.com>
---
 arch/arm64/Kconfig.platforms | 2 ++
 1 file changed, 2 insertions(+)

(Resending as I missed ALKML before)
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
!PM_GENERIC_DOMAINS, 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
!PM_GENERIC_DOMAINS

Can you please pick this for v4.8 directly ?

Regards,
Sudeep

v1->v2: Also added PM_GENERIC_DOMAINS dependency as suggested by Arnd[3]

[1] http://marc.info/?l=linux-pm&m=146607608629880&w=2
[2] https://marc.info/?l=linux-arm-kernel&m=146522896503670&w=2
[3] https://marc.info/?l=linux-arm-kernel&m=146619230406662&w=2

diff --git a/arch/arm64/Kconfig.platforms b/arch/arm64/Kconfig.platforms
index 7ef1d05859ae..25c4595589af 100644
--- a/arch/arm64/Kconfig.platforms
+++ b/arch/arm64/Kconfig.platforms
@@ -160,6 +160,8 @@ config ARCH_VEXPRESS
 	bool "ARMv8 software model (Versatile Express)"
 	select ARCH_REQUIRE_GPIOLIB
 	select COMMON_CLK_VERSATILE
+	select PM
+	select PM_GENERIC_DOMAINS
 	select POWER_RESET_VEXPRESS
 	select VEXPRESS_CONFIG
 	help
--
2.7.4