[PATCH v8 7/8] platform/chrome: Introduce device tree hardware prober

[Andy Shevchenko]

On Tue, Oct 08, 2024 at 03:34:26PM +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 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.

...

> +#include <linux/array_size.h>
> +#include <linux/errno.h>
> +#include <linux/i2c-of-prober.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>

> +static int chromeos_i2c_component_prober(struct device *dev, const void *_data)
> +{
> +	const struct chromeos_i2c_probe_data *data = _data;
> +	struct i2c_of_probe_simple_ctx ctx = {
> +		.opts = data->opts

Leave trailing comma in such cases (when it's not a terminator and
not on the same line with the variable definition).

> +	};
> +
> +	return i2c_of_probe_component(dev, data->cfg, &ctx);
> +}
> +
> +static const struct chromeos_i2c_probe_data chromeos_i2c_probe_dumb_touchscreen = {
> +	.cfg = &(const struct i2c_of_probe_cfg) {

Perhaps you can introduce something like

#define DEFINE_I2C_OF_PROBE_CFG(_type_, _ops_)		\
	(struct ...) {					\
		.ops = _ops_,				\
		.type = #_type_,			\
	}

and use it here as

	.cfg = DEFINE_I2C_OF_PROBE_CFG(touchscreen, NULL),

> +		.type = "touchscreen"

Ditto.

> +	}

Ditto.

> +};
> +
> +static const struct i2c_of_probe_cfg chromeos_i2c_probe_simple_trackpad_cfg = {
> +	.ops = &i2c_of_probe_simple_ops,
> +	.type = "trackpad"

Leave a comma.

> +};

...

> +static const struct chromeos_i2c_probe_data chromeos_i2c_probe_hana_trackpad = {
> +	.cfg = &chromeos_i2c_probe_simple_trackpad_cfg,

	.cfg = DEFINE_I2C_OF_PROBE_CFG(trackpad, i2c_of_probe_simple_ops),

Or even

#define DEFINE_I2C_OF_PROBE_CFG_SIMPLE(_type_)			\
	DEFINE_I2C_OF_PROBE_CFG(type, &i2c_of_probe_simple_ops)

> +	.opts = &(const struct i2c_of_probe_simple_opts) {

Perhaps also DEFINE_xxx for this compound literal?

> +		.res_node_compatible = "elan,ekth3000",
> +		.supply_name = "vcc",
> +		/*
> +		 * ELAN trackpad needs 2 ms for H/W init and 100 ms for F/W init.
> +		 * Synaptics trackpad needs 100 ms.
> +		 * However, the regulator is set to "always-on", presumably to
> +		 * avoid this delay. The ELAN driver is also missing delays.
> +		 */
> +		.post_power_on_delay_ms = 0,
> +	}
> +};
> +
> +static const struct hw_prober_entry hw_prober_platforms[] = {
> +	{ .compatible = "google,hana", .prober = chromeos_i2c_component_prober, .data = &chromeos_i2c_probe_dumb_touchscreen },
> +	{ .compatible = "google,hana", .prober = chromeos_i2c_component_prober, .data = &chromeos_i2c_probe_hana_trackpad },

These strings are a bit long, perhaps wrap on one member per line?

> +};

-- 
With Best Regards,
Andy Shevchenko