Linux 5.9 rc1 Is Released With Support for Upcoming AMD GPUs and Corsair RGB Hubs

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The merge window for Linux 5.9 is slammed shut with the first release candidate becoming available yesterday. The next Linux kernel will support using zstd compression for the kernel and initramfs images, 64-bit inodes on tmpfs file systems stored in memory and a whole range of new hardware. Support for two upcoming AMD graphics card families code-named "Sienna Cichlid" and "Navy Flounder" as well as support for the Corsair iCUE Commander Pro "smart" fan and RGB controller stand out as particularly interesting.

written by 林慧 (Wai Lin) 2020-08-17 - last edited 2020-08-18. © CC BY

Linux kernel 5.9.0rc1-neo.jpg
Linux 5.9 rc1.

Kernel chief Linus Torvalds had this to say about the first Linux 5.9 release candidate:

"This merge window felt a lot more normal than 5.8, and all the stats confirm thar it seems to be the usual size.

The only thing that stands out is yet another AMD GPU header file drop, but by now that almost counts as "usual" too. It does mean that the diff stats are dominated by those AMD updates, and almost exactly half of the diff is under drivers/gpu/drm/amd/, but it's the usual big register definitions (presumably once more generated from the hw files) and doesn't really matter in the big picture.

If you ignore that, stats look very normal. Even ignoring the AMD GPU updates, drivers are still about 60% of the patch, and it's all over. Outside of drivers, it's the usual mix of architecture updates, documentation, core networking, tooling and filesystem updates.

"Normal size" is still obviously pretty big, so the appended is just my merge-log as usual. For details, dig down into whichever area excites you in the git tree..."

Linus Torvalds on the Linux Kernel Mailing List
August 16th, 2020

New AMD Graphics Cards

The very huge AMD graphics driver patches added to Linux 5.9 brings support for two different AMD graphics card families: "Sienna Cichlid" and "Navy Flounder". These will use an entirely new display core (support is named "Display Core Next 3.0", DRM_AMD_DC_DCN3_0) and they will have a brand new hardware video decoding ASIC called "Video Core Next 3.0" to go along with it. That makes those cards distinctly different from AMDs existing Navi (DCN 2.0) and Renoir (DCN 2.1) graphics chips. That they are very different is evident from some of the new driver files like amdgpu/sdma_v5_2.c where they are referred to as CHIP_SIENNA_CICHLID and CHIP_NAVY_FLOUNDER. The existing Navi GPU family is referred to as CHIP_NAVI10, CHIP_NAVI12, CHIP_NAVI14 and so on in their amdgpu/sdma_v5_0.c driver. The upcoming "Sienna Cichlid" and "Navy Flounder" cards are not just re-branded Navi cards, there are some big differences between them in the driver code.

Our AMD sources were very tight-lipped about these new "Sienna Cichlid" and "Navy Flounder" graphics chips. All they would admit was that:

"They should arrive late this year, and I don't expect them to be widely available until next year"

AMD source

AMD has also added hardware video decoding support for the now 10+ years old Northern Islands (Radeon HD6450-HD7670) series graphics cards to the amdgpu driver in this release. These old cards have so far only had hardware video decoding support in the older radeon driver. The radeon is stable and it works fine but it does not support vulkan. Those using older AMD graphics hardware have, so far, had to choose between hardware video decoding OR vulkan support.

There are also several other fixes for existing cards in the amdgpu driver. Runtime power management is now enabled on Vega 10 cards with BACO support, the swSMU code has been cleaned up and the DCN bandwidth calculation code has seen several fixes.

Linux 5.9 rc1 on a AMD Athlon 5350.

Linux 5.9 rc1 produces a series of RIP errors in the kernel's ring buffer (dmesg) on certain older APUs, just like the 5.8-series kernels do (5.7-series are fine in this regard). Alex Deucher from the AMD open source team has informed us that there is a patch for this issue pending in the Kernel DRM miscellaneous fixes and cross-tree. It will likely get merged by the time Linux 5.9 is released and it will get back-ported to the next 5.8-series release.

zstd Support For Compressing The Kernel And Initramfs

The kernel has had support for the zstd compression algorithm for some time. It can now use that support to compress the kernel itself and initramfs images using zstd. The kernel will be compressed using compression level -19 when zstd is used (set in scripts/Makefile.lib line 444). It will be up to the user-space programs for creating initramfs images to decide if those will let end-users decide. zstd can compress very fast and inefficient or compress very slowly and be very efficient depending on what compression level you go for. zstd decompression is really fast regardless of what compression level was used to compress a file.

The kernel will not check if you have the zstd binary installed if you choose to compress the kernel using it and it won't notify you when it fails to compress a bzImage if you do not have it installed but you will find out when you try to make install.

The Linux kernel has had support for compressing zswap and file systems (notibly btrfs and squashfs) using zstd for some time.

New Drivers

A close-up inspection of the kernel's commit log reveals a lot of new drivers beyond those related to new AMD graphics cards.

There is now support for NVMe Target Passthrough (NVME_TARGET_PASSTHRU) using the NVMe Over Fabrics protocol for NVMe drivers that allow the host system to manage the NVMe controller directly.

The USB version of the "Infrared Toy and IR Droid" (IR_TOY) IR transmitter is now supported.

There are two new WiFi drivers for wireless chips from an outfit calleld "Microchip": Atmel WILC1000 SDIO and Atmel WILC1000 SPI are now supported.

There are also new drivers for Silex Insight BA431 and Silex Insight BA431 random number generators.

Many of the drivers added to recent kernel releases have been Android-specific and this release-cycle is no different. There are drivers for the TI BQ2515X battery charger family found on some wearable devices, the DW9768 camera lens, the Maxim Integrated MAX98373 Speaker Amplifier and the DisplayPort on the Xilinx ZynqMP SoC.

Corsair Commander PRO RGB

Nothing says "processional" like a rig with dozens of blinking RGB lights. The iCUE Commander is a small fan and RGB hub that lets you connect a bunch of fans with or without RGB lights on them. Some of Corsairs cases come with it. It can also be bought separately on their website.

Professionals can enjoy Linux support for the Corsair iCUE Commander PRO Smart RGB Lighting and Fan Speed Controller (SENSORS_CORSAIR_CPRO) when Linux 5.9 is released.

New Intel Emmitsburg SoC And Rocket Lake GPU Support

Linux 5.9 supports pin control, GPIO, I2C and MFD on new Intel chipset called "Emmitsburg". Support for "Emmitsburg" has also been added to the Intel Trace Hub driver. drivers/pinctrl/intel/pinctrl-emmitsburg.c and drivers/hwtracing/intel_th/pci.c so not reveal any interesting details about what kind of SoC "Emmitsburg" will be when it is released. Intel tends to add support for new platforms long before they are released to the public so don't expect to see any products based on this SoC before the seconds half of 2021.

Intel has also added support for Rocket Lake to the i915 Intel graphics driver.

Linux 5.9 rc1 boots fine on our Intel-powered notebook with a Intel Pentium N4200 Goldmont processors. The machine will randomly hang without both the ahci.mobile_lpm_policy=1 and intel_idle.max_cstate=1 kernel command line parameters, just like all previous kernels do on that particular machine. Linux 5.9 rc1 will simply fail to boot on our Lenovo laptop with a Broadwell Core i7-5500U processor. Previous kernels, including 5.8.1, work fine on that machine. We can only guess if it has to do with changes to the i915 driver for 8th generation Intel graphics or some other change in Linux 5.9 rc1.

Linux 5.9 rc1 appears to work just fine on AMD powered desktop machines with older Polaris-series graphics cards (RX 470/RX 570). Machines with older AMD APUs are another story.

Linux 5.9 won't be released for another month so you will have to wait a while if you want any of the new drivers and features it contains. Brave users can download and compile the first release candidate from You should only do that if you are very curious or really need something 5.9rc1 has to offer. Stick with the kernel your distribution provides or compile a stable-branch kernel if you can't live with a fair chance of encountering random crashes, kernel panics and other issues. You may even find that 5.9 rc1 won't boot on your machine. Those kinds of problems aren't very common during a new kernel's release-cycle, but they do happen.

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