Hi, On Tue, Oct 8, 2024 at 12:35 AM Chen-Yu Tsai <wenst@xxxxxxxxxxxx> 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 prober. For any 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. > > Signed-off-by: Chen-Yu Tsai <wenst@xxxxxxxxxxxx> > Acked-by: Tzung-Bi Shih <tzungbi@xxxxxxxxxx> > --- > Maintainer expects this to be merged through I2C tree. > > Changes since v7: > - Corrected Makefile item order > - Replaced "failed-needs-probe" with "fail-needs-probe" in commit message > - Added include of "linux/of.h" for of_machine_is_compatible() > - Switched to simple probe helpers for trackpads on Hana > > Changes since v6: > - Adapted to new I2C OF prober interface > - Collected Acked-by > > Changes since v5: > - Adapt to new i2c_of_probe_component() parameters > > Changes since v4: > - Fix Kconfig dependency > - Update copyright year > - Drop "linux/of.h" header > - Include "linux/errno.h" > - Move |int ret| declaration to top of block > - Return -ENODEV on no match instead of 0 > - Unregister platform driver and device unconditionally after previous > change > > Changes since v3: > - Include linux/init.h > - Rewrite for loop in driver probe function as suggested by Andy > - Make prober driver buildable as module > - Ignore prober errors other than probe deferral > > Changes since v2: > - Addressed Rob's comments > - Move remaining driver code to drivers/platform/chrome/ > - Depend on rather than select CONFIG_I2C > - Copy machine check to driver init function > - Addressed Andy's comments > - Explicitly mention "device tree" or OF in driver name, description > and Kconfig symbol > - Drop filename from inside the file > - Switch to passing "struct device *" to shorten lines > - Move "ret = 0" to just before for_each_child_of_node(i2c_node, node) > - Make loop variable size_t (instead of unsigned int as Andy asked) > - Use PLATFORM_DEVID_NONE instead of raw -1 > - Use standard goto error path pattern in hw_prober_driver_init() > > - Changes since v1: > - New patch > --- > drivers/platform/chrome/Kconfig | 11 ++ > drivers/platform/chrome/Makefile | 1 + > .../platform/chrome/chromeos_of_hw_prober.c | 140 ++++++++++++++++++ > 3 files changed, 152 insertions(+) Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
