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    SubjectRe: [PATCH v4 4/4] i2c: Add multi-instantiate pseudo driver
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    On 2018-08-08 11:08, Andy Shevchenko wrote:
    > 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

    I don't see why a guard is needed? *Your* code below needs it, but that
    issue is not a concern for the original code. It might however be a
    good idea to fail the probe if there are no clients to instantiate, but
    that's a different issue...

    >
    > 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).

    I think using two allocations is a waste in this case.

    >
    >> +
    >> + 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

    But not as flexible/future-proof. Why should 0 be the only valid IRQ index?

    Cheers,
    Peter

    >> + 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
    >>
    >
    >
    >

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