[PATCH 2/3] arm64: dts: juno: add arm, primecell-periphid override
sudeep.holla at arm.com
Thu Jun 16 07:42:27 PDT 2016
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
So I raised the issue with !CONFIG_PM option and it was suggested to
make platform select the same as there's no simple way to deal with
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
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