On Thu, Oct 17, 2024 at 05:34:38PM +0800, Chen-Yu Tsai wrote: > Some devices are designed and manufactured with some components having > multiple drop-in replacement options. These components are often > connected to the mainboard via ribbon cables, having the same signals > and pin assignments across all options. These may include the display > panel and touchscreen on laptops and tablets, and the trackpad on > laptops. Sometimes which component option is used in a particular device > can be detected by some firmware provided identifier, other times that > information is not available, and the kernel has to try to probe each > device. > > This change attempts to make the "probe each device" case cleaner. The > current approach is to have all options added and enabled in the device > tree. The kernel would then bind each device and run each driver's probe > function. This works, but has been broken before due to the introduction > of asynchronous probing, causing multiple instances requesting "shared" > resources, such as pinmuxes, GPIO pins, interrupt lines, at the same > time, with only one instance succeeding. Work arounds for these include > moving the pinmux to the parent I2C controller, using GPIO hogs or > pinmux settings to keep the GPIO pins in some fixed configuration, and > requesting the interrupt line very late. Such configurations can be seen > on the MT8183 Krane Chromebook tablets, and the Qualcomm sc8280xp-based > Lenovo Thinkpad 13S. > > Instead of this delicate dance between drivers and device tree quirks, > this change introduces a simple I2C component probe function. For a > given class of devices on the same I2C bus, it will go through all of > them, doing a simple I2C read transfer and see which one of them responds. > It will then enable the device that responds. > > This requires some minor modifications in the existing device tree. The > status for all the device nodes for the component options must be set > to "fail-needs-probe". This makes it clear that some mechanism is > needed to enable one of them, and also prevents the prober and device > drivers running at the same time. ... > +#include <linux/cleanup.h> > +#include <linux/device.h> > +#include <linux/dev_printk.h> > +#include <linux/err.h> > +#include <linux/i2c.h> > +#include <linux/i2c-of-prober.h> > +#include <linux/module.h> > +#include <linux/of.h> > +#include <linux/slab.h> In case you need a new version, also add stddef.h for NULL definition. -- With Best Regards, Andy Shevchenko
