SoC (System on a Chip)

The perpetual effort to make the Linux kernel work on any piece of hardware available is ongoing. This work takes place within projects like OpenWrt and also within companies that design, manufacture, or sell hardware and products based on Linux. Much of this work eventually gets mainlined, meaning the code becomes part of the mainline Linux kernel.

Today, we take wireless functionality for granted, but in the beginning, it was a real challenge. The IEEE 802.11 family of standards inspired what could be achieved, but the available Linux kernel drivers were poorly written, lacked features, or didn't exist. This is still true for some of the wireless hardware on the market today. No matter how fantastic or powerful a device may be, its Linux drivers offer limited functionality.

Since its founding, OpenWrt has focused on customer premise equipment (CPE) hardware such as routers and NAS devices, dedicating much effort to supporting IEEE 802.11 as extensively as possible. Given that the initial hardware, the Linksys WRT54G, sold over 400,000 units in its first months, it's safe to say that the work done by the OpenWrt project has had an impact.

Most SoC manufacturers license a (soft or hard) IP core for a certain CPU design from a licensor like MIPS or ARM, then combine this with other (self-developed or licensed) (soft or hard) IP cores for DSP-, wireless-, VoIP-, Sound-, Switch-, etc-functionality and commission the manufacturing of Chips at some semiconductor foundry. These Chips, SoCs, are acquired by different manufacturers of Routers. The latter design PCBs for whatever purpose and solder the purchased chips (SoC, RAM, Flash) onto them.

Company	CPU				IP for Mixed-signal integrated circuit
	Intruction set license for			own IP	wired			optical	wireless
	MIPS	ARM	Power Architecture	other	Ethernet	DSL	DOCSIS	GPON	802.11	WiMAX	LTE
Broadcom	MIPS32, MIPS64	ARMv6, ARMv7, ARMv8			✔	✔	✔		✔
Marvell (Intel)		ARMv5 (XScale, Sheeva), ARMv6, ARMv7			✔				✔
Qualcomm (Atheros, ZyDAS)	MIPS32	ARMv5, ARMv6, ARMv7		Ubicom32, Ubicom64	✔				✔
MediaTek (Ralink)	MIPS32	ARMv5, ARMv6, ARMv7			✔	✔			✔
Lantiq (Infineon, Texas Instruments)	MIPS32				✔	✔			✔
Samsung		ARMv4, ARMv5, ARMv6, ARMv7
Texas Instuments		ARMv5, ARMv6, ARMv7		TMS320	✔
Ikanos (Conexant, Analog Devices)	MIPS32, Lexra	ARMv5, ARMv6				✔
Realtek	Lexra, MIPS32				✔	✔			✔
Intel (Digital Equipment Corporation) (Texas Instruments)		ARMv4 (StrongARM), ARMv5 (XScale), ARMv6		x86, x86-64, IA-64	✔		✔		✔
AMD	MIPS32, MIPS64	ARMv8?		x86, x86-64
Apple		ARMv7
Hisilicon		ARMv?
Cavium Networks	MIPS32, MIPS64	ARMv4
Vitesse Semiconductor
Applied Micro Circuits Corporation		ARMv8	✔
Maxim Integrated
Freescale Semiconductor		ARMv5, ARMv6, ARMv7	✔	Motorola 68000
Allwinner Technology		ARMv5, ARMv7, ARMv8
Renesas Electronics	MIPS64	ARMv7		SuperH ,M32R
Sony	MIPS?		✔
Toshiba	MIPS?
SiFive				RISC-V

2002-04-29: AMD Adopts MIPS Technologies’ 64-BIT Architecture

Cavium CNS1202: Cisco RVS4000 v2
Mindspeed Comcerto-SoC: ZyXEL NBG5715
Qualcomm Ubicom32: D-Link DIR-657 HD Media Router 1000
Conexant/Ikanos CX94610-11Z: Xavi 7968
Freescale MPC85xx PowerQUICC III P1014@800MHz TP-Link TL-WDR4900 v1, v1.3

Now that we have an overview over the companies that own/license semiconductor IP, let's have a look of the available support of their products in the mainline Linux kernel or in the OpenWrt Linux kernel. We don't much care about the Android Linux kernel or about heavily modified (and outdated) Linux kernels.

TODO

For mainlined Linux kernel-drivers for the

IEEE 802.3 (Ethernet) cf. ?
- E.g. BCM63xx codebase with GPL'd Ethernet and USB support proves, that sometimes FOSS drivers for Ethernet NICs are not available.
IEEE 802.11 cf. Comparison of open-source wireless drivers and http://wireless.kernel.org/en/users/Drivers
DSL is a Layer1 protocol; as Layer2 protocol usually ATM is employed. Cf. PPPoEoA vs. PPPoE to PPPoA. Long story short, we require support for ATM in the Linux kernel:
- /net/atm/Kconfig
- Documentation/atm.txt
For the Lantiq xDSL support cf. soc.lantiq. Any better sources?
FOSS support for the Broadcom DSL-IP does not exist.
FOSS support for the Ikanos/Conexant DSL-IP does not exist.

Each different OpenWrt platform represents a set of hardware that share certain common features, such as being part of the same family of SoCs. Depending on the semiconductor company that designs the SoC, a SoC-family can consist entirely of IP blocks that are all well-supported, maybe already mainlined. But it can also contain IP blocks, for that only raggedly written, feature-poor code exists, that would never be mainlined. Or IP blocks that are completely unsupported by the Linux kernel.