On Fri, Sep 13, 2024 at 12:25 PM Andy Shevchenko
[off-list ref] wrote:

On Wed, Sep 11, 2024 at 03:27:44PM +0800, Chen-Yu Tsai wrote:

quoted

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 "failed-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.

...

quoted

+static int i2c_of_probe_enable_node(struct device *dev, struct device_node *node)
+{
+     int ret;

quoted

+     dev_info(dev, "Enabling %pOF\n", node);

Is it important to be on INFO level?

Not really.

quoted

+     struct of_changeset *ocs __free(kfree) = kzalloc(sizeof(*ocs), GFP_KERNEL);
+     if (!ocs)
+             return -ENOMEM;
+
+     of_changeset_init(ocs);
+     ret = of_changeset_update_prop_string(ocs, node, "status", "okay");
+     if (ret)
+             return ret;
+
+     ret = of_changeset_apply(ocs);
+     if (ret) {
+             /* ocs needs to be explicitly cleaned up before being freed. */
+             of_changeset_destroy(ocs);
+     } else {
+             /*
+              * ocs is intentionally kept around as it needs to
+              * exist as long as the change is applied.
+              */
+             void *ptr __always_unused = no_free_ptr(ocs);
+     }
+
+     return ret;
+}

...

quoted

+int i2c_of_probe_component(struct device *dev, const struct i2c_of_probe_cfg *cfg, void *ctx)
+{
+     const struct i2c_of_probe_ops *ops;
+     const char *type;
+     struct device_node *i2c_node;
+     struct i2c_adapter *i2c;
+     int ret;
+
+     if (!cfg)
+             return -EINVAL;
+
+     ops = cfg->ops ?: &i2c_of_probe_dummy_ops;
+     type = cfg->type;
+
+     i2c_node = i2c_of_probe_get_i2c_node(dev, type);

        struct device_node *i2c_node __free(of_node_put) =
                i2c_...;

cleanup.h says to not mix the two styles (scoped vs goto). I was trying
to follow that, though I realize now that with the scoped loops it
probably doesn't help.

I'll revert back to having __free().

quoted

+     if (IS_ERR(i2c_node))
+             return PTR_ERR(i2c_node);
+
+     for_each_child_of_node_with_prefix(i2c_node, node, type) {
+             if (!of_device_is_available(node))
+                     continue;
+
+             /*
+              * Device tree has component already enabled. Either the
+              * device tree isn't supported or we already probed once.
+              */
+             ret = 0;

Shouldn't you drop reference count for "node"? (See also below)

This for-each loop the "scoped". It just doesn't have the prefix anymore.
I believe you asked if the prefix could be dropped and then Rob agreed.

quoted

+             goto out_put_i2c_node;
+     }
+
+     i2c = of_get_i2c_adapter_by_node(i2c_node);
+     if (!i2c) {
+             ret = dev_err_probe(dev, -EPROBE_DEFER, "Couldn't get I2C adapter\n");
+             goto out_put_i2c_node;
+     }
+
+     /* Grab resources */
+     ret = 0;
+     if (ops->get_resources)
+             ret = ops->get_resources(dev, i2c_node, ctx);
+     if (ret)
+             goto out_put_i2c_adapter;
+
+     /* Enable resources */
+     if (ops->enable)
+             ret = ops->enable(dev, ctx);
+     if (ret)
+             goto out_release_resources;
+
+     ret = 0;
+     for_each_child_of_node_with_prefix(i2c_node, node, type) {
+             union i2c_smbus_data data;
+             u32 addr;
+
+             if (of_property_read_u32(node, "reg", &addr))
+                     continue;
+             if (i2c_smbus_xfer(i2c, addr, 0, I2C_SMBUS_READ, 0, I2C_SMBUS_BYTE, &data) < 0)
+                     continue;
+
+             /* Found a device that is responding */
+             if (ops->free_resources_early)
+                     ops->free_resources_early(ctx);
+             ret = i2c_of_probe_enable_node(dev, node);

Hmm... Is "node" reference count left bumped up for a reason?

Same as above.

quoted

+             break;
+     }
+
+     if (ops->cleanup)
+             ops->cleanup(dev, ctx);
+out_release_resources:
+     if (ops->free_resources_late)
+             ops->free_resources_late(ctx);
+out_put_i2c_adapter:
+     i2c_put_adapter(i2c);
+out_put_i2c_node:
+     of_node_put(i2c_node);
+
+     return ret;
+}

...

quoted

+/*
+ * i2c-of-prober.h - definitions for the Linux I2C OF component prober

Please avoid putting filenames inside files. In the possible future event of
file renaming this may become a burden and sometimes even forgotten.

Ack.

quoted

+ * Copyright (C) 2024 Google LLC
+ */
+
+#ifndef _LINUX_I2C_OF_PROBER_H
+#define _LINUX_I2C_OF_PROBER_H

quoted

+#if IS_ENABLED(CONFIG_OF_DYNAMIC)

Do you really need to hide data types with this? Wouldn't be enough to hide
APIs only?

Ack. Will move the data types outside.


Thanks
ChenYu

quoted

+struct device;
+struct device_node;
+
+/**
+ * struct i2c_of_probe_ops - I2C OF component prober callbacks
+ *
+ * A set of callbacks to be used by i2c_of_probe_component().
+ *
+ * All callbacks are optional. Callbacks are called only once per run, and are
+ * used in the order they are defined in this structure.
+ *
+ * All callbacks that have return values shall return %0 on success,
+ * or a negative error number on failure.
+ *
+ * The @dev parameter passed to the callbacks is the same as @dev passed to
+ * i2c_of_probe_component(). It should only be used for dev_printk() calls
+ * and nothing else, especially not managed device resource (devres) APIs.
+ */
+struct i2c_of_probe_ops {
+     /** @get_resources: Retrieve resources for components. */
+     int (*get_resources)(struct device *dev, struct device_node *bus_node, void *data);
+
+     /** @free_resources_early: Release exclusive resources prior to enabling component. */
+     void (*free_resources_early)(void *data);
+
+     /**
+      * @enable: Enable resources so that the components respond to probes.
+      *
+      * Resources should be reverted to their initial state before returning if this fails.
+      */
+     int (*enable)(struct device *dev, void *data);
+
+     /**
+      * @cleanup: Opposite of @enable to balance refcounts after probing.
+      *
+      * Can not operate on resources already freed in @free_resources_early.
+      */
+     int (*cleanup)(struct device *dev, void *data);
+
+     /**
+      * @free_resources_late: Release all resources, including those that would have
+      *                       been released by @free_resources_early.
+      */
+     void (*free_resources_late)(void *data);
+};
+
+/**
+ * struct i2c_of_probe_cfg - I2C OF component prober configuration
+ * @ops: Callbacks for the prober to use.
+ * @type: A string to match the device node name prefix to probe for.
+ */
+struct i2c_of_probe_cfg {
+     const struct i2c_of_probe_ops *ops;
+     const char *type;
+};
+
+int i2c_of_probe_component(struct device *dev, const struct i2c_of_probe_cfg *cfg, void *ctx);
+
+#endif /* IS_ENABLED(CONFIG_OF_DYNAMIC) */
+
+#endif /* _LINUX_I2C_OF_PROBER_H */

--
With Best Regards,
Andy Shevchenko