linux-kernel - Re: [PATCH v4 2/3] i2c: core: add device-managed version of i2c_new

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Date:   Fri, 15 Dec 2017 23:08:20 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>, Peter Rosin <peda@...ntia.se>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/3] i2c: core: add device-managed version of i2c_new_dummy

2017-12-15 18:44 GMT+01:00 Heiner Kallweit <hkallweit1@...il.com>:
> i2c_new_dummy is typically called from the probe function of the
> driver for the primary i2c client. It requires calls to
> i2c_unregister_device in the error path of the probe function and
> in the remove function.
> This can be simplified by introducing a device-managed version.
>
> Note the changed error case return value type:
> i2c_new_dummy returns NULL whilst devm_new_i2c_dummy returns an ERR_PTR.
>
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> Reviewed-by: Bartosz Golaszewski <brgl@...ev.pl>
> ---
> v2:
> - use new function _i2c_new_dummy with detailed error codes
> v3:
> - no changes
> v4:
> - reflect renaming to __i2c_new_dummy
> - add reviewed-by
> ---
>  Documentation/driver-model/devres.txt |  3 +++
>  drivers/i2c/i2c-core-base.c           | 38 +++++++++++++++++++++++++++++++++++
>  include/linux/i2c.h                   |  3 +++
>  3 files changed, 44 insertions(+)
>
> diff --git a/Documentation/driver-model/devres.txt b/Documentation/driver-model/devres.txt
> index c180045eb..6e2bccf85 100644
> --- a/Documentation/driver-model/devres.txt
> +++ b/Documentation/driver-model/devres.txt
> @@ -259,6 +259,9 @@ GPIO
>    devm_gpio_request_one()
>    devm_gpio_free()
>
> +I2C
> +  devm_i2c_new_dummy
> +
>  IIO
>    devm_iio_device_alloc()
>    devm_iio_device_free()
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 3b962456c..7a6669f07 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -864,6 +864,44 @@ struct i2c_client *i2c_new_dummy(struct i2c_adapter *adapter, u16 address)
>  }
>  EXPORT_SYMBOL_GPL(i2c_new_dummy);
>
> +static void devm_i2c_release_dummy(struct device *dev, void *res)
> +{
> +       i2c_unregister_device(*(struct i2c_client **)res);
> +}
> +
> +/**
> + * devm_i2c_new_dummy - return a new i2c device bound to a dummy driver
> + * @dev: device the managed resource is bound to
> + * @adapter: the adapter managing the device
> + * @address: seven bit address to be used
> + * Context: can sleep
> + *
> + * This is the device-managed version of i2c_new_dummy.
> + * Note the changed return value type: It returns the new i2c client
> + * or an ERR_PTR in case of an error.
> + */
> +struct i2c_client *devm_i2c_new_dummy(struct device *dev,
> +                                     struct i2c_adapter *adapter,
> +                                     u16 address)
> +{
> +       struct i2c_client *ret, **dr;
> +
> +       dr = devres_alloc(devm_i2c_release_dummy, sizeof(*dr), GFP_KERNEL);
> +       if (!dr)
> +               return ERR_PTR(-ENOMEM);
> +

While I understand that this pattern has been used before I still
think it's much less readable than using a separate devm struct
containing the i2c_client. Please take a look at kernel/irq/irq_sim.c:
while I may be biased since I added that code, I think it's cleaner to
avoid the casts and double pointers. Remember - we prefer readability
over saving three lines of code (and probably none in its compiled
form).

Thanks,
Bartosz

> +       ret = __i2c_new_dummy(adapter, address);
> +       if (IS_ERR(ret)) {
> +               devres_free(dr);
> +       } else {
> +               *dr = ret;
> +               devres_add(dev, dr);
> +       }
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(devm_i2c_new_dummy);
> +
>  /**
>   * i2c_new_secondary_device - Helper to get the instantiated secondary address
>   * and create the associated device
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 5d7f3c185..aca6ebbb8 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -441,6 +441,9 @@ extern int i2c_probe_func_quick_read(struct i2c_adapter *, unsigned short addr);
>  extern struct i2c_client *
>  i2c_new_dummy(struct i2c_adapter *adap, u16 address);
>
> +extern struct i2c_client *
> +devm_i2c_new_dummy(struct device *dev, struct i2c_adapter *adap, u16 address);
> +
>  extern struct i2c_client *
>  i2c_new_secondary_device(struct i2c_client *client,
>                                 const char *name,
> --
> 2.15.1
>
>