On Tue, Nov 01, 2022 at 03:20:26PM +0200, Tomi Valkeinen wrote:

From: Luca Ceresoli <luca@lucaceresoli.net>

An ATR is a device that looks similar to an i2c-mux: it has an I2C
slave "upstream" port and N master "downstream" ports, and forwards
transactions from upstream to the appropriate downstream port. But is
is different in that the forwarded transaction has a different slave
address. The address used on the upstream bus is called the "alias"
and is (potentially) different from the physical slave address of the
downstream chip.

Add a helper file (just like i2c-mux.c for a mux or switch) to allow
implementing ATR features in a device driver. The helper takes care or
adapter creation/destruction and translates addresses at each transaction.

...

    i2c-topology
    muxes/i2c-mux-gpio
    i2c-sysfs
+   muxes/i2c-atr

Doesn't make sense to group muxes/*, that they are following each other?

...

+I2C ADDRESS TRANSLATOR (ATR)
+M:	Luca Ceresoli [off-list ref]

Hmm... Are you going to maintain this? Or Review? Why not?

+L:	linux-i2c@vger.kernel.org
+S:	Maintained
+F:	drivers/i2c/i2c-atr.c
+F:	include/linux/i2c-atr.h

...

+		void *new_buf = kmalloc_array(num, sizeof(chan->orig_addrs[0]),
+					      GFP_KERNEL);
+		if (new_buf == NULL)
+			return -ENOMEM;

Isn't it better to write this as

		void *new_buf;

		new_buf = kmalloc_array(num, sizeof(chan->orig_addrs[0]), GFP_KERNEL);
		if (!new_buf)
			return -ENOMEM;

Remarks:
- note the style of the conditional
- why is it void?

Also, does it make sense to use krealloc_array() or is it complete replacement
of the data?

+		kfree(chan->orig_addrs);
+		chan->orig_addrs = new_buf;
+		chan->orig_addrs_size = num;

...

+static void i2c_atr_unmap_msgs(struct i2c_atr_chan *chan, struct i2c_msg msgs[],
+			       int num)

[] in the function parameter is longer than * and actually doesn't make
difference in C. Ditto for the rest of similar cases.

...

+static int i2c_atr_smbus_xfer(struct i2c_adapter *adap, u16 addr,
+			      unsigned short flags, char read_write, u8 command,
+			      int size, union i2c_smbus_data *data)

Can flags be fixed size (yes I understand that in our case short would probably
never be different to u16, but for the sake of clearness)?

...

+static int i2c_atr_attach_client(struct i2c_adapter *adapter,
+				 const struct i2c_board_info *info,
+				 const struct i2c_client *client)
+{
+	struct i2c_atr_chan *chan = adapter->algo_data;
+	struct i2c_atr *atr = chan->atr;
+	struct i2c_atr_cli2alias_pair *c2a;

+	u16 alias_id = 0;

Can we split assignment from the definition and locate it closer to the first
use?

+	int ret = 0;

Useless assignment.

+
+	c2a = kzalloc(sizeof(*c2a), GFP_KERNEL);
+	if (!c2a)
+		return -ENOMEM;
+
+	ret = atr->ops->attach_client(atr, chan->chan_id, info, client,
+				      &alias_id);

On one line looks better.

+	if (ret)
+		goto err_free;
+	if (alias_id == 0) {
+		ret = -EINVAL;
+		goto err_free;
+	}
+
+	c2a->client = client;
+	c2a->alias = alias_id;
+	list_add(&c2a->node, &chan->alias_list);
+
+	return 0;
+
+err_free:
+	kfree(c2a);
+	return ret;
+}

...

+int i2c_atr_add_adapter(struct i2c_atr *atr, u32 chan_id,
+			struct fwnode_handle *bus_handle)
+{
+	struct i2c_adapter *parent = atr->parent;
+	struct device *dev = atr->dev;
+	struct i2c_atr_chan *chan;
+	char *symlink_name;
+	int ret;
+
+	if (chan_id >= atr->max_adapters) {
+		dev_err(dev, "No room for more i2c-atr adapters\n");
+		return -EINVAL;
+	}
+
+	if (atr->adapter[chan_id]) {
+		dev_err(dev, "Adapter %d already present\n", chan_id);
+		return -EEXIST;
+	}
+
+	chan = kzalloc(sizeof(*chan), GFP_KERNEL);
+	if (!chan)
+		return -ENOMEM;
+
+	chan->atr = atr;
+	chan->chan_id = chan_id;
+	INIT_LIST_HEAD(&chan->alias_list);
+	mutex_init(&chan->orig_addrs_lock);
+
+	snprintf(chan->adap.name, sizeof(chan->adap.name), "i2c-%d-atr-%d",
+		 i2c_adapter_id(parent), chan_id);
+	chan->adap.owner = THIS_MODULE;
+	chan->adap.algo = &atr->algo;
+	chan->adap.algo_data = chan;
+	chan->adap.dev.parent = dev;
+	chan->adap.retries = parent->retries;
+	chan->adap.timeout = parent->timeout;
+	chan->adap.quirks = parent->quirks;
+	chan->adap.lock_ops = &i2c_atr_lock_ops;
+	chan->adap.attach_ops = &i2c_atr_attach_ops;
+
+	if (bus_handle) {
+		device_set_node(&chan->adap.dev, fwnode_handle_get(bus_handle));
+	} else {
+		struct fwnode_handle *atr_node;
+		struct fwnode_handle *child;
+		u32 reg;
+
+		atr_node = device_get_named_child_node(dev, "i2c-atr");
+
+		fwnode_for_each_child_node(atr_node, child) {
+			ret = fwnode_property_read_u32(child, "reg", &reg);
+			if (ret)
+				continue;
+			if (chan_id == reg)
+				break;
+		}
+
+		device_set_node(&chan->adap.dev, child);
+		fwnode_handle_put(atr_node);
+	}

It seems you have OF independent code, but by some reason you included of.h
instead of property.h. Am I right?

+	ret = i2c_add_adapter(&chan->adap);
+	if (ret) {
+		dev_err(dev, "failed to add atr-adapter %u (error=%d)\n",
+			chan_id, ret);
+		goto err_add_adapter;
+	}
+
+	symlink_name = kasprintf(GFP_KERNEL, "channel-%u", chan_id);

No NULL check?

+	WARN(sysfs_create_link(&chan->adap.dev.kobj, &dev->kobj, "atr_device"),
+	     "can't create symlink to atr device\n");
+	WARN(sysfs_create_link(&dev->kobj, &chan->adap.dev.kobj, symlink_name),
+	     "can't create symlink for channel %u\n", chan_id);

Why WARNs? sysfs has already some in their implementation.

+
+	kfree(symlink_name);
+
+	dev_dbg(dev, "Added ATR child bus %d\n", i2c_adapter_id(&chan->adap));
+
+	atr->adapter[chan_id] = &chan->adap;
+	return 0;
+
+err_add_adapter:
+	mutex_destroy(&chan->orig_addrs_lock);
+	kfree(chan);
+	return ret;
+}

...

+	struct fwnode_handle *fwnode = adap->dev.fwnode;

Please don't dereference fwnode like this, we have dev_fwnode() for that.

...

+	if (atr->adapter[chan_id] == NULL) {

!

+		dev_err(dev, "Adapter %d does not exist\n", chan_id);
+		return;
+	}

...

+	snprintf(symlink_name, sizeof(symlink_name),
+		 "channel-%u", chan->chan_id);

Once line?

...

+	atr_size = struct_size(atr, adapter, max_adapters);

+	if (atr_size == SIZE_MAX)
+		return ERR_PTR(-EOVERFLOW);

Dunno if you really need this to be separated from devm_kzalloc(), either way
you will get an error, but in embedded case it will be -ENOMEM.

+	atr = devm_kzalloc(dev, atr_size, GFP_KERNEL);
+	if (!atr)
+		return ERR_PTR(-ENOMEM);

...

+EXPORT_SYMBOL_GPL(i2c_atr_delete);

I would put these to their own namespace from day 1.


...

+/**
+ * Helper to add I2C ATR features to a device driver.
+ */

??? Copy'n'paste typo?

+struct i2c_atr {
+	/* private: internal use only */
+
+	struct i2c_adapter *parent;
+	struct device *dev;
+	const struct i2c_atr_ops *ops;
+
+	void *priv;
+
+	struct i2c_algorithm algo;
+	struct mutex lock;
+	int max_adapters;
+
+	struct i2c_adapter *adapter[0];

No VLAs.

+};

...

+int i2c_atr_add_adapter(struct i2c_atr *atr, u32 chan_id,
+			struct fwnode_handle *bus_np);

Missing

struct fwnode_handle;

at the top of the file?

-- 
With Best Regards,
Andy Shevchenko