RE: [PATCH 0/3] Add power domain driver support for i.mx8m family

[Aisheng Dong <aisheng.dong@nxp.com>]

> From: Jacky Bai
> Sent: Wednesday, April 17, 2019 1:27 PM
> 
> The i.MX8M family is a set of NXP product focus on delivering the latest and
> greatest video and audio experience combining state-of-the-art media-specific
> features with high-performance processing while optimized for lowest power
> consumption.
> i.MX8MQ, i.MX8MM, i.MX8MN, even the furture i.MX8MP are all belong to
> this family.
> 
> The GPC module is used to manage the PU power domains' power on/off. For
> the whole i.MX8M family, different SoC has differnt power domain design. the
> power up sequence has significant difference.
> all the power sequence must be guaranteed by SW. Some domains' power up
> sequence need to access the SRC module or sub-system specific GPR.
> the SRC register & SS's register are not in in the GPC's memory range.
> 
> it makes us hard to use the GPCv2 driver to cover all the different power up
> requirement. Each time, a new SoC is added, we must modify the GPCv2 driver
> to make it resuable for it. a lot of code need to be added in GPCv2 to support it.
> we need to access the SRC & SS' GPR, then the GPCv2 driver can NOT be
> self-contained. Accessing the non-driver specific module's register is a bad
> practice. Although, the GPC module provided the similar function for PU power
> domain, but it is not 100% compatible with GPCv2.
> 
> The most important thing is that the GPC & SRC module is a security critical
> resource that security permission must be considered when building the
> security system. The GPC module is not only used by PU power domain power
> on/off. It is also used by the TF-A PSCI code to do the CPU core power
> management. the SRC module control the CPU CORE reset and the CPU reset
> vector address. if we give the non-secure world write permission to SRC.
> System can be easily induced to malicious code.
> 

Considering the security issue, it looks to me a right direction to move GPC
power handling into ATF.
It also helps build a more generic driver and ease other OS integration
needed by customers (e.g. QNX, Win10).

Lucas,
How do you think of it?

Regards
Dong Aisheng

> This patchset add a more generic power domain driver that give us the
> possibility to use one driver to cover the whole i.MX8M family power domain
> in kernel side. kernel side doesn't need to handle the power domain difference
> anymore, all the sequence can be abstracted & handled in TF-A side. Most
> important, We don't need to care if the GPC & SRC is security protected.
> 
> Jacky Bai (3):
>   dt-bindings: power: Add power domain binding for i.mx8m family
>   soc: imx: Add power domain driver support for i.mx8m family
>   arm64: dts: freescale: Add power domain nodes for i.mx8mm
> 
>  .../bindings/power/fsl,imx8m-genpd.txt        |  46 ++++
>  arch/arm64/boot/dts/freescale/imx8mm.dtsi     | 103 ++++++++
>  drivers/soc/imx/Kconfig                       |   6 +
>  drivers/soc/imx/Makefile                      |   1 +
>  drivers/soc/imx/imx8m_pm_domains.c            | 224
> ++++++++++++++++++
>  include/soc/imx/imx_sip.h                     |  12 +
>  6 files changed, 392 insertions(+)
>  create mode 100644
> Documentation/devicetree/bindings/power/fsl,imx8m-genpd.txt
>  create mode 100644 drivers/soc/imx/imx8m_pm_domains.c
>  create mode 100644 include/soc/imx/imx_sip.h
> 
> --
> 2.21.0