[0/1,SRU,Bionic/raspi2] Add devicetree overlay for SLB9670 TPM module

BugLink: https://bugs.launchpad.net/bugs/1822036

[Impact]

Currently it is not possible to use the SLB9670 TPM module with Ubuntu
Core since we do not ship the required devicetree overlay to enable it
https://github.com/raspberrypi/linux/commit/c28ac2dc08bd73963f953a757a3362c64b5524ed
and there is no way for snaps to easily add their own devicetree
overlay. Finally it is not practical to expect Ubuntu Core users to have
to build and maintain their own kernels just to support a particular
hardware device.

For background discussion, refer to this thread on the snapcraft forums
https://forum.snapcraft.io/t/guidance-on-snap-interface-to-load-a-device-tree-overlay-on-rpi-core18/10106/11

Once this overlay is added, then users simply need to modify the boot
config.txt to enable the overlay to be loaded automatically. In the
future, snapd might also enable support so this can be managed by snapd
via snap system configuration.

[Test Case]

Boot a RPi with a SLB9670 connected, modify /boot/config.txt to specify
dtoverlay=tpm-slb9670, then load the tpm_tis_spi module and /dev/tpm0
should be available.

[Regression Potential]

Almost zero chance of regression potential since this is simply adding a
new overlay to the kernel. This is not loaded automatically so there is
no real chance of regression.

[Other Info]

All that is required for this SRU is to merge
https://github.com/raspberrypi/linux/commit/c28ac2dc08bd73963f953a757a3362c64b5524ed
to the current bionic raspi kernel branch.

Peter Huewe (1):
  Add overlay for SLB9760 Iridium /LetsTrust TPM

 arch/arm/boot/dts/overlays/Makefile           |  1 +
 arch/arm/boot/dts/overlays/README             |  8 ++++
 .../boot/dts/overlays/tpm-slb9670-overlay.dts | 44 +++++++++++++++++++
 3 files changed, 53 insertions(+)
 create mode 100644 arch/arm/boot/dts/overlays/tpm-slb9670-overlay.dts

On 2019-04-01 10:03:05 , Alex Murray wrote:
> BugLink: https://bugs.launchpad.net/bugs/1822036
> 
> [Impact]
> 
> Currently it is not possible to use the SLB9670 TPM module with Ubuntu
> Core since we do not ship the required devicetree overlay to enable it
> https://github.com/raspberrypi/linux/commit/c28ac2dc08bd73963f953a757a3362c64b5524ed
> and there is no way for snaps to easily add their own devicetree
> overlay. Finally it is not practical to expect Ubuntu Core users to have
> to build and maintain their own kernels just to support a particular
> hardware device.
> 
> For background discussion, refer to this thread on the snapcraft forums
> https://forum.snapcraft.io/t/guidance-on-snap-interface-to-load-a-device-tree-overlay-on-rpi-core18/10106/11
> 
> Once this overlay is added, then users simply need to modify the boot
> config.txt to enable the overlay to be loaded automatically. In the
> future, snapd might also enable support so this can be managed by snapd
> via snap system configuration.
> 
> [Test Case]
> 
> Boot a RPi with a SLB9670 connected, modify /boot/config.txt to specify
> dtoverlay=tpm-slb9670, then load the tpm_tis_spi module and /dev/tpm0
> should be available.
> 
> [Regression Potential]
> 
> Almost zero chance of regression potential since this is simply adding a
> new overlay to the kernel. This is not loaded automatically so there is
> no real chance of regression.
> 
> [Other Info]
> 
> All that is required for this SRU is to merge
> https://github.com/raspberrypi/linux/commit/c28ac2dc08bd73963f953a757a3362c64b5524ed
> to the current bionic raspi kernel branch.
> 
> Peter Huewe (1):
>   Add overlay for SLB9760 Iridium /LetsTrust TPM
> 
>  arch/arm/boot/dts/overlays/Makefile           |  1 +
>  arch/arm/boot/dts/overlays/README             |  8 ++++
>  .../boot/dts/overlays/tpm-slb9670-overlay.dts | 44 +++++++++++++++++++
>  3 files changed, 53 insertions(+)
>  create mode 100644 arch/arm/boot/dts/overlays/tpm-slb9670-overlay.dts
> 
> -- 
> 2.17.1
> 
> 
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