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Amlogic S905

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Amlogic S905/
S905-H
Amlogic S905
Amlogic S905
Manufacturer Amlogic
Name S905/
S905-H
Architecture aarch64
CPU 4x 2 GHz Cortex-A53
GPU Mali-450
Year 2015
Process 28nm
Mainline yes
Community Page https://linux-meson.com/
Components
CPU
Works
UART
Works
Storage
Partial
USB
Works
Display
Works
GPU
Works
Pinctrl
Works
I²C
Works
SPI
No data
Audio
Works
Video
Partial
Thermal
Works
NPU
No data
Suspend
Broken
Ethernet
No data
SATA
No data

The Amlogic S905, also known as Meson GXBB, is a fairly capable high-end media player SoC mainly used in Android set-top boxes. It's capable of hardware decoding up to 4K@60fps, for multiple formats including H.264, AVS+, and 10-bit, and part of the S9 family of Amlogic chipsets. It has great U-Boot and mainline Linux support, making it a great candidate for building a set-top box or single-board computer powered by postmarketOS.

There's also the Amlogic S905-H SoC, which merely just includes Dolby licenses.

Devices

Device Codename Chipset Mainline booting
Videostrong KII Pro videostrong-kii-pro Amlogic S905 Y Yes

Boot process

See: Amlogic#Boot process

BL1 looks for a header (named @AML header) at different offsets depending on the storage media:

  • On an SD card: offset 512 (512 bytes completly ignored by BL1), header and checksum from offset 528 to 623, payload at offset 4608 onwards
  • On eMMC: offset 0, header and checksum from offset 16 to 111, payload at offset 4096 onwards

The header roughly looks like this:

/*
 * Hex dump:
 * 00000000: 0000 0000 0000 0000 0000 0000 0000 0000  ................
 * 00000010: 4041 4d4c f0bf 0000 4000 0100 0000 0000  @AML....@.......
 * 00000020: 0000 0000 4000 0000 0002 0000 6000 0000  ....@.......`...
 * 00000030: 0000 0000 4002 0000 b00d 0000 90bf 0000  ....@...........
 * 00000040: 0000 0000 f00f 0000 00b0 0000 0000 0000  ................
 * 00000050: efe0 c669 d471 d507 27c2 9e5d d0ec 1b2b  ...i.q..'..]...+
 * 00000060: 1cdd f482 9acd 3606 ef35 301a ac48 0d7d  ......6..50..H.}
 */

/*
 * C struct
 */
struct aml_hdr {
    /* before magic word: random bytes ignored by BL1 */
	uint32_t magic; /* "@AML" */
	uint32_t total_size;
	uint8_t header_size;
	uint8_t root_key_index;
	uint8_t version_major;
	uint8_t version_minor;
	uint32_t padding1;
	uint32_t digest_type;
	uint32_t digest_offset;
	uint32_t digest_size;
	uint32_t data_offset;
	uint32_t key_type;
	uint32_t key_offset;
	uint32_t key_size;
	uint32_t data_size;
	uint32_t payload_type;
	uint32_t payload_offset;
	uint32_t payload_size;
	uint32_t padding2;
} __packed;

There's a bug where, because of the zero-offset requirement on eMMC, MBR structures cannot coexist, requiring tweaks to allow an MBR parition table to coexist. Further reading: https://github.com/LibreELEC/amlogic-boot-fip/pull/8

BL2 is signed by using a proprietary utility from Amlogic called aml_encrypt_gxb, for example:

$ aml_encrypt_gxb --bootsig --input boot_new.bin --output u-boot.img

There's a replacement for aml_encrypt_gxb called amlbootsig. See https://github.com/afaerber/meson-tools. For example, one could use:

$ amlbootsig boot_new.bin u-boot.img

It has been confirmed to work on ODROID-C2 and Videostrong KII Pro (videostrong-kii-pro).


Status

GPU and hardware acceleration

Works. Lima is used for hardware acceleration.

IR RX

Works. Aftermarket and original IR remotes are expected to work out of the box (as seen on Videostrong KII Pro (videostrong-kii-pro)). Doesn't require much configuration.

Audio

Works. Requires a device tree patch on the Videostrong KII Pro (videostrong-kii-pro), that adds the appropriate nodes (else the card is never pobed) which is slowly making its way upstream. HDMI audio works, but S/PDIF is untested.

Hardware decoding and encoding

See: https://libera.irclog.whitequark.org/linux-amlogic/2023-02-10

The Amlogic S905(-H) supports hardware decoding up to 4K@60fps, but in the mainline kernel it's limited to 1080p. Downstream kernels relied on lengthy hacks to get it working up to 4K, and thus they were not included in the mainline kernel (to their defense Amlogic did successfully enable 4K playback on 3.x kernels).

To get hardware encoding to work, refer to this issue comment. It boils down to:

There are some issues, however:

  • Needs non-free firmware
  • 10-bit media (e.g. 4K) won't work
  • MPEG1/2/4 support is broken

So sometimes you may want to resort to using software decoding.

Hardware encoding doesn't work yet.

Suspend

Broken

DVB

Needs a demux driver.

OTG

Untested. Broken according to linux-meson.com

U-Boot

Most (all?) set-top boxes based on this SoC use U-Boot as their primary bootloader, but mainline U-Boot has great support for this SoC. Running mainline U-Boot as the primary bootloader and as the secondary bootloader works fine. If you want to use U-Boot as the primary bootloader, refer to Videostrong KII Pro (videostrong-kii-pro)/U-Boot as primary bootloader, replacing mentions of wetek-play2 with your device or one close enough (which have RAM timings that work on your device). Please note that BL2 and BL30 are proprietary; there's an on-going effort on porting mainline Arm Trusted Firmware-A to Videostrong KII Pro (videostrong-kii-pro).

See also