Re: [PATCH 2/3] arm64: dts: juno: add arm,primecell-periphid override

On 06/06/16 16:59, Sudeep Holla wrote:

The Linux AMBA 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
those 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.

Since keeping the power domain on by default affects the core power(by
preventing cores entering deeper idle states), it's not feasible
solution. Instead we can provide arm,primecell-periphid override in the
device tree that prevents accessing the device early in the boot.

OK, I recently found out that AMBA bus/infrastructure can deal with 
powered off domains even while adding the devices. That makes this patch 
redundant. I had missed it initially as I tested with !CONFIG_PM
option.

So I raised the issue with !CONFIG_PM option[1] and it was suggested to 
make platform select the same[2] as there's no simple way to deal with
that.

Hence I will drop this patch but will post patch to select PM from
ARCH_VEXPRESS to ensure we always have it enabled to deal with this
platform issue.

-- 
Regards,
Sudeep


[1] http://marc.info/?l=linux-pm&m=146607608629880&w=2
[2] http://marc.info/?l=linux-pm&m=146608125731479&w=2
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