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

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Wed, Aug 8, 2018 at 11:30 AM, Hans de Goede <hdegoede@redhat.com> 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?

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

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).

> +
> +       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@redhat.com>");
> +MODULE_LICENSE("GPL");
> --
> 2.18.0
>



-- 
With Best Regards,
Andy Shevchenko