Hello and Welcome to the blog on “HiKey970 Mainlining Update - Part 2”. This blog will summarise the recent mainlining efforts for HiKey970 board in Linux kernel.
HiKey970 is the first 96Boards from the HiKey family to join the 96Boards.ai initiative. The HiKey970 features the HiSilicon Kirin 970 SoC with HiAI Architecture and a dedicated NPU. Stacked with LPDDR4X 1866MHz memory, 64GB UFS 2.1 storage, Bluetooth ® wireless technology, WIFI, GPS among many other features, this board is made for developers, looking maximize accelerated AI capabilities. Since this board falls under the CE Extended Edition form factor, it offers interfaces such as Ethernet port, PCIE-Mini connector, PCIE M.2 connector, on-board UART, CAN port etc…
The Kirin970(Hi3670) SoC is just a superset of Hi3660 SoC with an added AI processing element.
Reset Controller support
Once the initial SoC and board support patches are merged mainline, I started working on the Reset controller support. Reset controller in HI3670 SoC is exposed under the clock controller register mapping. So, we need to reuse the clock register base, which is done using System Controller (Syscon) node. Since the HI3670 SoC is architecturally same as HI3660 SoC, we can reuse the same reset controller driver. So, I added a new compatible for the HI3670 SoC and submitted the first version of the patchset.
But I got a comment from the reset maintainer to use the DT fallback approach instead of creating a new compatible which does nothing. For those who don’t know what DT compatible fallback approach, it is nothing but adding a dummy DT compatible to the node and adding a second compatible. So if the first compatible driver is not found, the node (device) will bound to the driver with second compatible. This way, we can avoid adding dummy compatibles to the driver. By incorporating his review comment, I posted the second version of the patchset which got Acked by the maintainer.
Link to Patchset: https://lkml.org/lkml/2019/2/15/10
UFS Controller support
Next, I targeted the Universal Flash Storage (UFS) controller for booting a distro from a non-volatile memory. As like reset controller, the UFS controller is almost same with the HI3660 SoC, but with a subtle difference in the PHY layer used. HI3670 SoC uses the 10nm PHY. So, with the modifications required to handle the 10nm PHY, I submitted the UFS patchset to the mailing list. It took a while for getting a maintainer to review this patchset since the original UFS maintainer vanished. Finally, the driver and bindings patches are accepted by the maintainer following the Ack from HiSi dev.
Link to Patchset: https://patchwork.ozlabs.org/cover/1020952/
SD and WiFi support
Finally, I decided to add the SD card and WiFi support. This required me to add the Designware MMC controller support for this SoC. As like the former subsystems, this was also same as that of HI3660 SoC. Hence, I just added the required DT nodes with DT compatible fallback approach and submitted to the mailing list. For getting the WiFi to work, one has to place the TI connectivity firmware to
Link to Patchset: https://lkml.org/lkml/2019/2/28/888
At the end, we have the HiKey970 board booting a distro with mainline linux kernel from UFS or SD card with WiFi :-) Still there are plenty of features to be added in order to get a fully functional board support in mainline. So stay tuned for the updates and happy hacking!