Re: [PATCH v4 2/8] i2c: add I2C Address Translator (ATR) support

Andy Shevchenko
2022-11-01T14:31:10Z

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 <luca@lucaceresoli.net>

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