Re: [PATCH v4 4/4] i2c: Add multi-instantiate pseudo driver

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Hi,

On 08/08/2018 11:08 AM, Andy Shevchenko wrote:
On Wed, Aug 8, 2018 at 11:30 AM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
On systems with ACPI instantiated i2c-clients, normally there is 1 fw_node
per i2c-device and that fw-node contains 1 I2cSerialBus resource for that 1
i2c-device.

But in some rare cases the manufacturer has decided to describe multiple
i2c-devices in a single ACPI fwnode with multiple I2cSerialBus resources.

An earlier attempt to fix this in the i2c-core resulted in a lot of extra
code to support this corner-case.

This commit introduces a new i2c-multi-instantiate driver which fixes this
in a different way. This new driver can be built as a module which will
only loaded on affected systems.

This driver will instantiate a new i2c-client per I2cSerialBus resource,
using the driver_data from the acpi_device_id it is binding to to tell it
which chip-type (and optional irq-resource) to use when instantiating.

Note this driver depends on a platform device being instantiated for the
ACPI fwnode, see the i2c_multi_instantiate_ids list of ACPI device-ids in
drivers/acpi/scan.c: acpi_device_enumeration_by_parent().

Thanks for an update! My comments below.

+struct i2c_inst_data {
+       const char *type;
+       int irq_idx;
+};

+struct i2c_multi_inst_data {

+       int no_clients;

Name a bit confusing. What about num_clients?

no is often used as abbreviation for "number of" so this is a quite
normal naming scheme. But if you really want me to I can do a v5
renaming this to num_clients.


+       struct i2c_client *clients[0];
+};
+
+static int i2c_multi_inst_probe(struct platform_device *pdev)
+{
+       struct i2c_multi_inst_data *multi;
+       const struct acpi_device_id *match;
+       const struct i2c_inst_data *inst_data;
+       struct i2c_board_info board_info = {};
+       struct device *dev = &pdev->dev;
+       struct acpi_device *adev;
+       char name[32];
+       int i, ret;
+
+       match = acpi_match_device(dev->driver->acpi_match_table, dev);
+       if (!match) {
+               dev_err(dev, "Error ACPI match data is missing\n");
+               return -ENODEV;
+       }
+       inst_data = (const struct i2c_inst_data *)match->driver_data;
+
+       adev = ACPI_COMPANION(dev);
+

+       /* Count number of clients to instantiate */
+       for (i = 0; inst_data[i].type; i++) {}
+
+       multi = devm_kmalloc(dev,
+                       offsetof(struct i2c_multi_inst_data, clients[i]),
+                       GFP_KERNEL);
+       if (!multi)
+               return -ENOMEM;

Here I see the following:
  - it's kinda unusual use of offsetof()

There are actually plenty of places doing this, this is the normal way
to get the size of a struct which ends with a variable sized array.

I would prefer to keep this as is.

, perhaps i*sizeof() + sizeof()
would be more understandable
  - there is no guard against i == 0

i depends on the driver_data, defining a driver_data
where i == 0 is silly, still if this happens nothing bad
will happen, so I see no need for a check for this.


To solve both, it might be like

struct i2c_multi_inst_data {
        int num_clients;
        struct i2c_client *clients;
};

...
multi = devm_kmalloc(sizeof(*multi), GFP_KERNEL);
if (!multi)
  return -ENOMEM;

multi->clients = devm_kcalloc(i, sizeof(*multi->clients), GFP_KERNEL);
if (ZERO_PTR_OR_NULL(multi->clients))
  return -ENOMEM;

But I would like to hear your (other's) opinion(s).

Nack for this option, this just makes the code more
complicated and uses allocs instead of 1 for no good
reason IMHO.

Regards,

Hans



+
+       multi->no_clients = i;
+
+       for (i = 0; i < multi->no_clients; i++) {
+               memset(&board_info, 0, sizeof(board_info));
+               strlcpy(board_info.type, inst_data[i].type, I2C_NAME_SIZE);
+               snprintf(name, sizeof(name), "%s-%s", match->id,
+                        inst_data[i].type);
+               board_info.dev_name = name;
+               board_info.irq = 0;

+               if (inst_data[i].irq_idx != -1) {

= 0 sounds more robust

+                       ret = acpi_dev_gpio_irq_get(adev, inst_data[i].irq_idx);
+                       if (ret < 0) {

+                               dev_err(dev, "Error requesting irq at index %d: %d\n",
+                                       inst_data[i].irq_idx, ret);

irq -> IRQ in the message.

+                               goto error;
+                       }
+                       board_info.irq = ret;
+               }
+               multi->clients[i] = i2c_acpi_new_device(dev, i, &board_info);
+               if (!multi->clients[i]) {
+                       dev_err(dev, "Error creating i2c-client, idx %d\n", i);
+                       ret = -ENODEV;
+                       goto error;
+               }
+       }
+
+       platform_set_drvdata(pdev, multi);
+       return 0;
+
+error:

+       while (--i >= 0)

It can be simple

while (i--)

+               i2c_unregister_device(multi->clients[i]);
+
+       return ret;
+}
+
+static int i2c_multi_inst_remove(struct platform_device *pdev)
+{
+       struct i2c_multi_inst_data *multi = platform_get_drvdata(pdev);
+       int i;
+
+       for (i = 0; i < multi->no_clients; i++)
+               i2c_unregister_device(multi->clients[i]);
+
+       return 0;
+}
+
+static const struct i2c_inst_data bsg1160_data[]  = {
+       { "bmc150_accel", 0 },
+       { "bmc150_magn", -1 },
+       { "bmg160", -1 },
+       {}
+};
+
+/*
+ * Note new device-ids must also be added to i2c_multi_instantiate_ids in
+ * drivers/acpi/scan.c: acpi_device_enumeration_by_parent().
+ */
+static const struct acpi_device_id i2c_multi_inst_acpi_ids[] = {
+       { "BSG1160", (unsigned long)bsg1160_data },
+       { }
+};
+MODULE_DEVICE_TABLE(acpi, i2c_multi_inst_acpi_ids);
+
+static struct platform_driver i2c_multi_inst_driver = {
+       .driver = {
+               .name = "I2C multi instantiate pseudo device driver",

+               .acpi_match_table = ACPI_PTR(i2c_multi_inst_acpi_ids),

We don't need ACPI_PTR for the driver which depends on ACPI.
In the general case we have an inconsistency with variable definition
(might be unused).

+       },
+       .probe = i2c_multi_inst_probe,
+       .remove = i2c_multi_inst_remove,
+};
+module_platform_driver(i2c_multi_inst_driver);
+
+MODULE_DESCRIPTION("I2C multi instantiate pseudo device driver");
+MODULE_AUTHOR("Hans de Goede <hdegoede@xxxxxxxxxx>");
+MODULE_LICENSE("GPL");
--
2.18.0







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