On Mon, Dec 20, 2021 at 1:49 PM Dmitry Torokhov <dtor@xxxxxxxxxxxx> wrote: > > Hi Paul, > > On Mon, Dec 20, 2021 at 1:07 PM Paul Menzel <pmenzel@xxxxxxxxxxxxx> wrote: > > > > From: Furquan Shaikh <furquan@xxxxxxxxxx> > > > > Dear Linux folks, > > > > > > Google Chromebooks are often built with devices sourced from different > > vendors. These need to be probed. To deal with this, the firmware – in > > this case coreboot – tags such optional devices accordingly – I think > > this is commit fbf2c79b (drivers/i2c/generic: Add config for marking > > device as probed) – and Chromium OS’ Linux kernel has the patch at hand > > applied to act accordingly. Right after the merge, Dmitry created a > > revert, which was actively discussed for two days but wasn’t applied. > > That means, millions of devices shipped with such a firmware and Linux > > kernel. To support these devices with upstream Linux kernel, is there an > > alternative to applying the patch to the Linux kernel, and to support > > the shipped devices? > > *sigh* I should have pushed harder, but I see it managed to > proliferate even into our newer kernels. Not having this patch should > not cause any problems, it can only hurt, because the i2c core has no > idea how to power up and reset the device properly. The only downside > of not having this patch is that we may have devices in sysfs that are > not connected to actual hardware. They do now cause any problems and > is how we have been shipping ARM-based devices where we also dual- and > triple-source components. However if we were to have a device that > switches between several addresses (let's say device in bootloader > mode uses 0x10 address and in normal mode 0x20) this "probing" may > result in device not being detected at all. > > If we wanted to do this correctly, coreboot would have to implement > full power and reset control and also add drivers for I2C controllers > to be able to communicate with peripherals, and then adjust _STA > methods to report "not present" when the device is indeed absent. And > note that even in this case we would have issues with "morphing > devices", so coreboot would also need to know how to reset device out > of bootloader mode, and maybe flash firmware so device can work in > normal mode. > > However coreboot does (or did?) not want to add code to handle i2c > controllers, and would like to push this knowledge to the kernel. And > the kernel does know how to handle peripherals properly, but that > knowledge lies in individual drivers, not i2c core. > > We should remove "linux,probed" from coreboot and not propagate to > newer Chrome OS kernels, and keep it away from upstream. > Revert from chromeos-5.15 is at https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3350347. Everyone please feel free to comment there. Guenter
