This effort is also a continuation of my ongoing personal interest in these platforms, especially in mobile form factors such as widely-available tablets. Although I am no longer involved with contributing on the technical side of Replicant, I still care for the project and would like to see it move forward. Finding new developers for Replicant is hard and it's fair to say that a large part of the project is kept alive by its community of users and contributors. The project inherits from its upstream (currently LineageOS, that counts more developers by far), but a significant number of adaptations have to be introduced to workaround the use of proprietary blobs for hardware support, for each and every new version and device we want to support.
In the free software community, most of the effort related to liberating hardware support in a sustainable and future-proof direction happens (sometimes inadvertently so) in upstream projects such as Linux, coreboot and U-Boot. These projects usually drag more than enough contributions to keep their maintainers busy. Since features are added through a code review process (that requires submitting clean and maintainable code in the first place), the set of features supported by mainline is slow to pick-up with downstream modified versions provided by manufacturers, that are used instead in Replicant. For the mobile use cases that we aim to cover, the constraints are high in terms of required features and power management. This is why it did not seem like a good idea to ship mainline Linux in Replicant at first. However, using downstream software components has a cost in terms of maintenance (no kernel updates), security (no kernel updates) or long-term sustainability and compatibility with newer technologies (still no kernel updates). The amount of required time spent dealing with code where only the very minimum amount of structure and conventionality is in place is also very significant.
After a while working on Replicant, I became more and more reluctant to dedicate time to new contributions, mainly for the fact that I had to deal with downstream code that was just very unpleasant. It also felt like all the time and effort put-in could only ever have a very short term impact. That the level of contributed software support was only useful as long as the Android and Linux versions stayed relevant (and well, we can't say that they stay relevant for a very long time for these use cases).
This is why I was dragged more and more towards mainline software.
A Plea for Upstream Software
The effort to liberate hardware support is much more significant with mainline, but these contributions do tag along and stay, as long as there are people to care for them. The decisions regarding the code in future versions are also taken by the community instead of a single entity, although the community may also take decisions detrimental to freedom in digital technology. With mainline support landed in Linux, the userspace interfaces for systems are standardized and much less work has to be put-in on the userspace side (or more precisely, it only has to be done once and incrementally updated with new features). This means less involvement required on the Replicant side, with the ultimate goal of making Replicant a sheer rebranding of Lineage OS without proprietary blobs and using only generic Hardware Abstraction Layers (HALs) shared across Android systems. The Android-x86 project already has such HALs for various aspects of userspace software support (some of which where developed by companies like Intel that stick close to mainline), but there is still work left to do to adapt these HALs for mobile uses cases. Since these could benefit any Android system, it would be interesting to bring a coordinated effort for supporting mainline kernel interfaces through generic Android HALs (something an entity like Linaro could care for). This would allow redirecting the development effort for hardware support away from the downstream userspace side of Android systems and focused on mainline instead. Of course, mainline support also benefits other GNU/Linux systems and opens up the possibility of properly supporting mobile use cases in these systems, while also enabling new use cases.Purism is currently working in that direction, with projects to integrate KDE and GNOME-based interfaces to a mobile telephony-enabled device. Running GNU/Linux on mobile devices is not exactly new though, as a first wave of interest rose around 2008 from the Openmoko community, revolving around the Neo FreeRunner phone running with GNU/Linux. One of the systems supporting that phone was SHR (for Stable Hybrid Release) that was based on the Freesmartphone.org (FSO) framework for mobile devices and went on to support other devices such as the N900 or the Nexus S. But just like with the original systems for the FreeRunner, using regular GNU/Linux applications on SHR was hard and required using a stylus. The interface was obviously not designed nor adapted for the mobile use case, just like plenty of other system components. On the kernel side, the amount of changes required for the FreeRunner made the upstreaming process slow (and it was still not fully completed to this day).
The GTA01 development device, the Neo FreeRunner (GTA02) and the GTA04
Nowadays mobile devices revolve around the ARM instruction set (and the very commonly found ARM Cortex core implementations from the company) and ARM support in the mainline Linux kernel has come a long way since 2008. Most notably, the introduction of the OpenFirmwaredevice-tree (initially designed for supporting PowerPC devices) allowed a clean distinction between the hardware description and the drivers, which were previously glued together in (plenty of) platform data initialization laid out directly in the source code. Back then, adding support for a new device was tedious and each kernel had to be compiled for a precise device. Device-tree changed the game here, as it became much easier to introduce new device-specific support and possible at all to run the same kernel binary on different devices with the same ARM instruction set. This also made platform bringup a more streamlined task (by easily reusing similar blocks from previous generations and applying appropriate quirks at run-time). The number of supported ARM platforms, features and use cases kept on increasing, with the commitment of big companies like TI, Samsung, Google, ARM, Freescale/NXP or Rockchip, entities like Linaro or the linux-sunxi community but also smaller players (often providing upstreaming services to companies) like Bootlin (formerly Free Electrons), Collabora or Pengutronix. While most of the supported platforms are not ready for conventional mobile use cases yet, some come close and already offer support for a reduced number of use cases.
Signature Verifications Gone Wrong
Despite free software support in Linux, some platforms are fatally flawed when it comes to the boot software they are running. This is the case with enforced boot software signature verifications with missing keys, where the circuitry of the platform validates the digital signature of the first software running at boot with a public key stored in read-only memory. If the signature was not created using the (missing) private key associated with the public key, the platform will simply refuse to boot. A significant number of ARM platforms, such as the ones made by Qualcomm (Snapdragon and others), Amlogic or Samsung (Exynos) are plagued by enforced boot software signature verifications with missing keys. While signature verifications are a really good thing to have, it only makes sense if the user of the device has access to the associated keys. When the keys are kept secret by the manufacturer of the device or the platform, the whole security model of the device is delegated to this third party. The user cannot decide of their own security model and consider potential threats based on their own situation, that may not set this third party as a fully trusted peer. Instead, the implemented security model only covers this third party's threat model, that is designed to consider the user as a threat. While it might sound very odd, this is the result of enforcing technical limitations such as DRM, that are designed to forbid the user from accessing the unlocked raw multimedia contents.
LG Security Error
This modus operandi looks very similar to what a parent would do to prevent their newborn child from wandering around during night time: applying a technical restriction such as bars on the infant's bed. This is perfectly fine when the individual subjected to the restriction is not able to decide what is good for themselves. But when it comes to individuals with that capacity, imposing such intentional restrictions designed to serve this third party's interests first and foremost feels very inappropriate. But that's not the end of it: this limitation removes the practical possibility for the user to replace the software signed by these missing keys, making it proprietary software de-facto. It sometimes occurs that free copylefted software is used in devices that enforce such signature verifications, as it first occurred with the Tivo (and coined the name Tivoization for the process). Even with source code and the appropriate compilers available, only intermediate forms of software can be obtained. The product form of software (that is the form adapted for practical use) is intrinsically tied to the processing unit that executes the associated software instructions. This is why the practical ability to install the generated intermediate form into the code storage from where the code is executed (effectively making it the product form of the software) is an absolute requirement. When signature verifications are enforced, the part of the installation process related to signing the binaries (so that they can be executed) is missing. The software thus never reaches its product form, leaving the user with freedom over the source and intermediate forms of the software but not over its product form. As a result, the software cannot be considered to be free as a whole, although its license says so.
Current Status of Free Upstream Support
Thankfully, a number of ARM platforms are not flawed in this manner and allow running free boot software. Examples of such platforms include Allwinner, Rockchip, i.MX, OMAP GP and Tegra (without keys burned). U-Boot is widely used on devices with these platforms and manufacturers often use modified downstream versions based off ancient upstream releases. The associated source code for both U-Boot and Linux is not always available, although these projects are covered by a copyleft license. And when it does, it often takes the form of a board support package tarball with no version control information. Some parts of the code required for hardware support can also come missing or be voluntarily moved out of copylefted projects (something that Android seems to vastly encourage). This is often the case with DRAM initialization and features related to multimedia. Nevertheless, these source releases are useful and often allow adding mainline support for these devices.
The Google OP1 (Rockchip RK3399) as found on the Samsung Chromebook Plus
At this point in time, the platforms mentioned and many of the devices that use them are supported, to a more or less advanced degree, by upstream free software. Many significant tasks are still ahead of us, but there is work in progress going at a good rate. Support for Vivante GPUs (found in i.MX platforms) was merged and is being improved with time. There is also work in progress for both Mali Utgard, with the revival of the Lima project and Mali Midgard/Bifrost, with the Panfrost project that concerns a number of platforms such as Allwinner and Rockchip. Multimedia features in Linux are also work in progress, with the introduction of the media request API that will allow supporting stateless VPUs (that don't have a dedicated processor, nor require any firmware) in the V4L2 framework, coupled with the MEM2MEM framework that already allows supporting stateful VPUs such as the one found on Exynos and the i.MX6 platform (that require a proprietary loaded firmware). Support for stateless VPUs has been working in progress on the Rockchip side, with a reference driver available on the Chromium OS kernel tree, using an early proposal of the media request API, as well as an early driver from developer Ayaka, in addition to the reference Rockchip kernel driver. On the Tegra side of things, developer digetix from the Grate project has been working on VPU support for early generations of Tegra, that should apply to newer generations with limited effort. On Allwinner, VPU support is work in progress and a number of versions of the Sunxi-Cedrus VPU driver have been submitted already.
Innards of an i.MX6 CuBox-i
In addition to VPUs support, a number of image processing units are made available (especially so on Rockchip) with features ranging from colorspace conversion, and scaling to 2D operations like bit blit and porter-duff alpha blending. Some of this processing is useful for general-purpose image processing, like colorspace conversion and scaling and seems relevant to the V4L2 subsystem, while 2D operations seem more relevant for the DRM subsystem. There seems not to be much support for 2D operations acceleration through generic DRM interfaces in regular userspace implementations from freedesktop.org. Support for such acceleration in compositors would allow significantly speeding up these operations without resorting to the GPU. Since GPUs in graphics cards are often required for video features in x86 systems, it has become a common assumption that GPU support is available for all types of graphical operations. Needless to say that GPU support on ARM is still work in progress and that it is currently generally not available without proprietary software (especially on the many platforms that embed Mali or PowerVR GPUs). Moreover, using the GPU is not power-efficient compared to dedicated hardware components and sometimes does not even perform as fast.
However, the DRM subsystem already leverages plane overlays, that each have their own framebuffer and position on the CRTC and are blended by the hardware before hitting the encoder, as a single frame. But planes support in Xorg is currently not as easy thing to implement, especially when it comes to showing YUV 420 video frames in a dedicated plane. The historical approach for supporting this use case consists in setting a color key on the display hardware, that sets a particular color to alpha, and blend the result with the video frame, that integrates with the rest of the display contents. One downside is that the coloured box bounding the video plane has to follow the movements of the window displaying it, so some coordination is required. This coordination as well as color-keying was historically provided by the Xv extension to the X server. Alas, this extension relies on buffer copies, introducing a significant bottleneck in performance and sharing buffers directly is a much preferred approach nowadays (that wade possible with DMABUF handles). Thankfully, DRI3 and Wayland bring solutions to the issues found on Xorg.
Other features related to multimedia are slowly picking up support in Linux, with support for media pipelines and camera sensor input controllers. Other specific features also require significant effort, such as proper power management (a crucial feature on mobile devices). With all these developments happening, the idea of running mobile devices on upstream free software with a significant set of features allowing usual daily use cases slowly becomes a reality. These days, embedded mobile devices only seem to get more and more diversified: from laptops to phones and tablets, they are nowadays found in all sorts of form factors such as convertible laptops, single-board computers, mini PCs, dongles, home automation equipment or even connected surveillance, car and action cameras. All these new use cases are running with wild downstream software that causes a great deal of issues in terms of freedom and privacy/security. The proposed solution to allowing a somewhat sane use of this technology clearly has to start with upstream software support. Some of these products and use cases are not necessarily a good thing to have on a society-wide scale, but provided that they do exist, we might as well try and sanitize the technology that supports these new use cases.
Covering a New Interesting Use Case
When going through some of the latest released devices on Chinese marketplaces like Aliexpress or GearBest, I noticed a number of 4K action cameras featuring Wi-Fi and HDMI. With an ever-renewed interest for finding out about the guts of unusual devices (well, come to think of it, of usual devices too), I ran through the specs and found that the SoC is an Allwinner V3. One that probably has the VPU that I am writing support for. One that also has an 8M pixel sensor and a wide-angle lense attached, screaming to be piped to the VPU's encoder. But unfortunately, one that is not yet supported in upstream U-Boot and Linux. Thankfully, the community was quick to pick-up support for the V3s SoC from Allwinner. It was contributed to mainline U-Boot and Linux by linux-sunxi community member Icenowy, who has also designed a board using the V3s. The V3s is an integrated LQFP package grouping 64 MiB of DDR2 DRAM and the same processor and controllers as Allwinner's V3 SoC.
Allwinner V3 SoC
In the past, Allwinner has already released chips with minor variations under different names, such as the A10s matching the A13 or the R16 matching the A33. These chips share nearly the exact same set of registers as the platforms they are based on (if not the very same), so when it came to adding support for them in U-Boot and Linux, only a minimal amount of work was required. With V3s support in good shape in free upstream hardware support projects, adding bringing up the V3 based on the existing V3 support with a device in hands looks like a rather reasonable task.
And so I clicked and typed and clicked and typed until I received a little package with my name on it and a F60 Action Camera inside. Next up in the process: discovering and documenting the components used in the camera, starting with a hardware teardown!
Over the past months, I've been looking at moving my computing setups to more freedom-respecting ones. Currently, both the laptop and desktop that I use for doing serious work (read: writing code) are based on recent Intel platforms and run with a proprietary UEFI/BIOS. I initially made that choice to be able to run a fully free system, such as Trisquel, since Intel platforms come with fully free GPU drivers that don't require additional non-free firmwares and are officially supported by the manufacturer. Support for most other aspects of the hardware is also close to being flawless, so this makes the whole user experience really nice. However, it goes without saying that things aren't actually all that pretty, given that there is still a proprietary UEFI/BIOS in there, CPU micro-code updates, firmwares for e.g. the USB3 (xHCI) controller (all of which are pushed by the UEFI/BIOS) as well as a management engine (ME) and Intel's active management technology (AMT). So it all looks pretty from an operating system perspective, but things aren't at all pretty under the hood. All that brings serious concerns for privacy/security, but this is not really what I am the most concerned about, personally.
Recently, I got to appreciate running with a fully free bootloader when working on various aspects of U-Boot, the popular free software bootloader that is widely used on embedded devices, when freeing some of those devices “from the ground up”. However, I am not really using any of those devices (e.g. single board computers) that I am working on, since they simply aren't a good fit for doing any serious work on them. I tried using some as home-theater PC, but the state of the art of free software support doesn't allow that use case yet. Hopefully, we will one day be able to run Kodi on those: there are promising leads on the i.MX6 platform with Etnaviv and hardware-accelerated video decoding, despite using a proprietary firmware. On the other hand, Allwinner platforms have some hardware video decoding support, both reverse engineered by the sunxi community and released by Allwinner, but I couldn't get it to work sufficiently well to allow watching a full 720p movie. Perhaps the lack of proper graphics acceleration is to blame here, I can't really tell (and there is already some 2D acceleration for Xorg). Qualcomm platforms do have some nice graphics acceleration and 3D support thanks to Rob Clark's work on freedreno, but those platforms don't allow running a free bootloader since the bootrom enforces a signature check on it, which is a no-go for me. On the other hand, I recently found out that using mesa and llvmpipe on the most powerful devices does bring a significant change, but it is still not packaged with Debian on armhf!
Still, those boards remain good for some other use cases, such as powering the servers that I use for hosting various services that I use on the Internet. This is actually one of the reasons why I got involved in working with embedded hardware, and those devices are still as good a fit as they were back when I started playing around with them. In addition, now that I started freeing mobile devices such as the LG Optimus Black (P970) and Allwinner tablets, I may also use those with Replicant. I got used to using the Galaxy Note 2 (N7100), that has a proprietary and signed bootloader, as my main phone after a year or so of daily use, but it's probably not too late to switch to a more freedom-respecting one, even if I'll probably miss some aspects of the big Samsung device. Either way, using the device I'm currently working on is one of the best ways to ensure that it's actually usable.
So this opens doors for liberating some aspects of my use of computing, but the computers I am using the most daily, my laptop and desktop, still remain fatally flawed. I have been looking at the list of devices supported by Coreboot for a long time and now that Libreboot came around, it's even easier to get an idea of what laptops and mainboards can run with fully free software, or close. At this point, the laptops supported by Libreboot are simply too old to fit my use case. I need something that can handle building a Replicant image in a decent time, that is an hour or so, without running out of memory. Thus, I wondered what could come closest to being fully free, both regarding software executed on the main processor and firmwares running in separate chips. Among the most recent boards supported by Coreboot, I decided to skip the Intel ones, since their ME is nearly impossible to disable or liberate (it is signed). In addition, not all of those have free native DRAM initialization and free video BIOS support, despite developers' truly great efforts there. Thus, I started looking at boards based on AMD platforms, the other half of x86 platforms as they exist today. A little while ago, AMD made a nice move forward by freeing their AGESA BIOS reference code for inclusion in Coreboot, which supports recent chipsets (I was told they have decided to stop contributing, though). The code itself is a nightmare to work with and the fact that it's used as-is in Coreboot doesn't make development a particularly fun time, but at least, it's there. And it allowed developers to add support for a few interesting boards that are rather recent. A few interesting desktop motherboards are there and one particularly caught my attention: the F2A85-M. At the time of writing, a slightly different version of it, the F2A85-M PRO is still being sold brand new in (French) online shops, so it's very easy to get. Former Replicant developer GNUtoo and I decided to get one each and get Coreboot running on it as soon as possible. Apparently, someone already attempted that port in the past, but gave up without publishing all the work in progress patches. Only code for the Super I/O (that is different from the non-PRO version of the board) was found, so we still have to figure out what the other differences between the F2A85-M and the F2A85-M PRO are to properly support it in Coreboot. Getting in touch with the original developer who gave up could come-in handy for this.
Among the boards supported by Coreboot (thanks to the AMD AGESA code) is a laptop matching my expectations: the Lenovo G505s. It is somewhat similar to the F2A85-M, only that it trades its Super I/O for an embedded controller, a better fit for a laptop and its required power management constraints. Both of these come with a Radeon GPU inside the CPU (and if I got it right, some versions of the G505s also have another Radeon GPU on-board), which also holds the northbridge by the way. At this point, the Radeon GPU cannot be used out of the box without both a non-free video BIOS (that is a blob executing instructions to set up the video card at UEFI/BIOS time) and a non-free firmware. However, that situation could probably be improved.
Since we're stuck with the Radeon card on the G505s, there is very little choice but to use the video BIOS (it also holds necessary bits for the radeon driver to work). One might also prefer not to use the proprietary firmware that runs in the GPU and avoid the radeon driver at all, but this will end up in using VBE (VESA BIOS extensions), that callbacks to the video BIOS in the end. Of course, on such a powerful laptop, using llvmpipe instead of radeon as mesa backend can be painless for many use cases.
On the other hand, the F2A85-M has full PCI-e ports, so one can plug-in an external nVidia card that is supported by nouveau, the free software graphics driver for those. Display support in Coreboot still requires the non-free video BIOS (and it also has some bits that are needed by nouveau). In addition, the nouveau driver also requires a firmware to run on the card, but it was freed for the card that I decided to settle for, a GeForce 610 with 2 GiB RAM. Early tests report that it should cope just fine with the things I do on that desktop computer (gnome-shell, flightgear and some more).
In addition to full-size desktop and laptops, I also got myself interested in smaller (and more traveler-friendly) form factors on which I can still do significant work. I have been looking at Chromebooks for some time now, especially because they ship with Coreboot and free software on the embedded controller, which is quite unique. However, up until recently, all the Chromebooks needed proprietary software to boot up (for various bits on Intel x86 platforms or because the bootrom was enforcing a signature check with a manufacturer key that cannot be replaced on ARM platforms). However, Google recently released a batch of Chromebooks based on the Rockchip RK3288 SoC (the veyron family), that is known (thanks to the rockchip community and the various makers of community-friendly hardware based on Rockchip chips) to not enforce such signature checks. Thus, it allows running a free bootloader as early as possible. The C201 Chromebook by Asus was released a few months ago with a RK3288 SoC, so I decided to get one of those and see what we can do with it. The goal is to port Libreboot to it and so far, the results have been very positive: that's the machine that I am currently using to type this post and it's running with fully free software from the bootloader (Coreboot) up to the operating system. All the micro-controllers I'm using on it are also running free software (that is, using an external ath9k_htc Wi-Fi dongle). The security model implemented is truly great, kudos to the Chromium OS developers for it! I was indeed able to replace the keys inside the RO part of the SPI flash memory, sign a kernel with my own keys and have a verified boot setup that way!
All that stuff keep me busy (and sadly, makes me way behind on Replicant-related work), so stay tuned for more details on specific aspects of those things!