I have been contacted by email last week by a Linux user, probably noticing my recent patch for the gpio_it87 driver in the kernel. They have been hoping my driver could extend to IT7236 chips that are used in a number of gaming motherboards for controlling RGB LEDs.
Having left the case modding world after my first and only ThermalTake chassis – my mother gave me hell for the fans noise, mostly due to the plexiglass window on the side of the case – I still don’t have any context whatsoever on what the current state of these boards is, whether someone has written generic tools to set the LEDs, or even UIs for them. But it was an interesting back and forth of looking for leads into figuring out what is needed.
The first problem is, like most of you who already know a bit about electrical engineering and electronics, that clearly the IT7236 chip is clearly not the same series as the IT87xx chips that my driver supports. And since they are not the same series, they are unlikely to share the same functionality.
The IT87xx series chips are Super I/O controllers, which mean they implement functionality such as floppy-disk controllers, serial and parallel ports and similar interfaces, generally via the LPC bus. You usually know these chip names because these need to be supported by the kernel for them to show up in sensors output. In addition to these standard devices, many controllers include at least a set of general purpose I/O (GPIO) lines. On most consumer motherboards these are not exposed in any way, but boards designed for industrial applications, or customized boards tend to expose those lines easily.
Indeed, I wrote the gpio_it87 driver (well, actually adapted and extended it from a previous driver), because the board I was working on in Los Angeles had one of those chips, and we were interested in having access to the GPIO lines to drive some extra LEDs (and possibly in future versions more external interfaces, although I don’t know if anything was made of those). At the time, I did not manage to get the driver merged; a couple of years back, LaCie manufactured a NAS using a compatible chip, and two of their engineers got my original driver (further extended) merged into the Linux kernel. Since then I only submitted one other patch to add another ID for a compatible chip, because someone managed to send me a datasheet, and I could match it to the one I originally used to implement the driver as having the same behaviour.
Back to the original topic, the IT7236 chip is clearly not a Super I/O controller. It’s also not an Environmental Control (EC) chip, as I know that series is actually IT85xx, which is what my old laptop had. Somewhat luckily though, a “Preliminary Specifications” datasheet for that exact chip is available online from a company that appears to distribute electronics component in the general sense. I’m not sure if that was intentional or not, but having the datasheet is always handy of course.
According to these specifications, the IT7236xFN chips are “Touch ASIC Cap Button Controllers”. And indeed, ITE lists them as such. Comparing this with a different model in the same series shows that probably LED driving was not their original target, but they came to be useful for that. These chips also include an MCU based on a 8051 core, similarly to their EC solution — this makes them, and in particular the datasheet I found earlier, a bit more interesting to me. Unfortunately the datasheet is clearly amended to be the shorter version, and does not include a programming interface description.
Up to this point this tells us exactly one thing only: my driver is completely useless for this chip, as it implements specifically the Super I/O bus access, and it’s unlikely to be extensible to this series of chips. So a new driver is needed and some reverse engineering is likely to be required. The user who wrote me also gave me two other ITE chip names found on the board they have: IT87920 and IT8686 (which appears to be a PWN fan controller — I couldn’t find it on the ITE website at all). Since the it87 (hwmon) driver is still developed out-of-kernel on GitHub, I checked and found an issue that appears to describe a common situation for gaming motherboards: the fans are not controlled with the usual Super I/O chip, but with a separate (more accurate?) one, and that suggests that the LEDs are indeed controlled by another separate chip, which makes sense. The user ran strings on the UEFI/BIOS image and did indeed find modules named after IT8790 and IT7236 (and IT8728 for whatever reason), to confirm this.
None of this brings us any closer to supporting it though, so let’s take a loop at the datasheet, and we can see that the device has an I²C bus, instead of the LPC (or ISA) bus used by Super I/O and the fan controller. Which meant looking at i2cdev and lsi2c. Unfortunately the output can only see that there are things connected to the bus, but not what they are.
This leaves us pretty much dry. Particularly me since I don’t have hardware access. So my suggestion has been to consider looking into the Windows driver and software (that I’m sure the motherboard manufacturer provides), and possibly figure out if they can run in a virtualized environment (qemu?) where I²C traffic can be inspected. But there may be simpler, more useful or more advanced tools to do most of this already, since I have not spent any time on this particular topic before. So if you know of any of them, feel free to leave a comment on the blog, and I’ll make sure to forward them to the concerned user (since I have not asked them if I can publish their name I’m not going to out them — they can, if they want, leave a comment with their name to be reached directly!).