Messages in this thread | | | Date | Fri, 4 Nov 2022 13:59:06 +0200 | Subject | Re: [PATCH v4 2/8] i2c: add I2C Address Translator (ATR) support | From | Tomi Valkeinen <> |
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Hi Andy,
On 01/11/2022 16:30, Andy Shevchenko wrote: > 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?
Ok.
> ... > >> +I2C ADDRESS TRANSLATOR (ATR) >> +M: Luca Ceresoli <luca@lucaceresoli.net> > > Hmm... Are you going to maintain this? Or Review? Why not?
We haven't discussed with Luca if he wants to maintain this (this is mostly his code). But, indeed, I should add my name there.
>> +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;
Ok.
> Remarks: > - note the style of the conditional > - why is it void?
No idea. I'll change it.
> > Also, does it make sense to use krealloc_array() or is it complete replacement > of the data?
The whole array will be rewritten, so we don't need to preserve the current data.
The buffer allocated here (i.e. orig_addrs) is only used for the duration of the i2c_atr_master_xfer(). So, we could allocate a new buffer for every xfer call, but to avoid that, we retain the old buffer. Any old data in the buffer can be discarded.
>> + 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.
Ok. I missed a few, it seems.
> ... > >> +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)?
The parameters and their types come from the ops in struct i2c_algorithm.
> ... > >> +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?
Actually, I don't think we need to initialize it at all. If attach_client() fails, we don't care about alias_id. If attach_client() succeeds, it _must_ return alias_id.
>> + int ret = 0; > > Useless assignment.
Yep.
>> + >> + 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.
I agree, but it doesn't fit into 80 characters. I personally think that's a too narrow a limit, but some maintainers absolutely require max 80 chars, so I try to limit the lines to 80 unless it looks really ugly.
>> + 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", ®); >> + 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?
Just an leftover from the conversion from of to fwnode.
>> + 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?
Right, missed that.
>> + 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.
True, and I can drop these if required. But afaics, sysfs_create_link only warns if there's a duplicate entry, not for other errors.
>> + >> + 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.
Ok.
> ... > >> + if (atr->adapter[chan_id] == NULL) { > > !
Yep.
>> + 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?
80 char limit here too. But I see that this is (kind of) broken. In the i2c_atr_add_adapter() I used dynamic alloc for the symlink_name, but here we still have the fixed size buffer.
> > ... > >> + 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.
Yep. Well... I kind of like it to be explicit. Calling alloc(SIZE_MAX) doesn't feel nice.
>> + 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.
What would be the namespace? Isn't this something that should be subsystem-wide decision? I have to admit I have never used symbol namespaces, and don't know much about them.
> > ... > >> +/** >> + * Helper to add I2C ATR features to a device driver. >> + */ > > ??? Copy'n'paste typo?
No idea where that is from... I'll fix it.
>> +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.
Ok.
I'm not arguing against any of the comments you've made, I think they are all valid, but I want to point out that many of them are in a code copied from i2c-mux.
Whether there's any value in keeping i2c-mux and i2c-atr similar in design/style... Maybe not.
>> +}; > > ... > >> +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?
Ok.
Tomi
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