Re: [PATCH v2 1/7] driver: introduce less error-prone dev_get_drvdata alternative

[Sascha Hauer <s.hauer@pengutronix.de>]

On Wed, Oct 07, 2020 at 11:50:52AM +0200, Ahmad Fatoum wrote:
> We use dev_get_drvdata to get the driver match data associated with a
> device. This has two shortcomings:
> 
>  - Linux has dev_get_drvdata too, which returns a private pointer for
>    driver specific info to associate with a device. We use dev->priv
>    (or more often container_of) for that in barebox instead
> 
>  - It nearly always involves a cast to a double pointer, which is
>    error-prone as size and alignment match need to be ensured
>    on the programmer's part and can easily be gotten wrong:
> 	enum dev_type type;
> 	dev_get_drvdata(dev, (const void **)&type); // UB!
> 
> Add a new function that instead of using a double pointer argument,
> returns the pointer directly:
> 
>  - For normal pointer driver data, no cast is necessary
>  - For integer driver data casted to a pointer for storage,
>    the cast is still necessary, but it's only a single pointer
>    this way
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

Applied, thanks

Sascha

> ---
> v1 -> v2:
>   - Changed second patch to use pointer instead of enum in match data
>     (Sascha)
>   - Changed third and fourth patch to return error on match with
>     driver name instead of assuming to be compatible with a default
>     type.
> ---
>  drivers/base/driver.c | 11 +++++++++++
>  include/driver.h      | 18 ++++++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/drivers/base/driver.c b/drivers/base/driver.c
> index 412db6c40699..3205bbc3c33b 100644
> --- a/drivers/base/driver.c
> +++ b/drivers/base/driver.c
> @@ -500,3 +500,14 @@ int dev_get_drvdata(struct device_d *dev, const void **data)
>  
>  	return -ENODEV;
>  }
> +
> +const void *device_get_match_data(struct device_d *dev)
> +{
> +	if (dev->of_id_entry)
> +		return dev->of_id_entry->data;
> +
> +	if (dev->id_entry)
> +		return (void *)dev->id_entry->driver_data;
> +
> +	return NULL;
> +}
> diff --git a/include/driver.h b/include/driver.h
> index 1961ab6ed9ea..e2886d051d4f 100644
> --- a/include/driver.h
> +++ b/include/driver.h
> @@ -540,8 +540,26 @@ int devfs_create_partitions(const char *devname,
>  #define DRV_OF_COMPAT(compat) \
>  	IS_ENABLED(CONFIG_OFDEVICE) ? (compat) : NULL
>  
> +/**
> + * dev_get_drvdata - get driver match data associated with device
> + * @dev: device instance
> + * @data: pointer to void *, where match data is stored
> + *
> + * Returns 0 on success and error code otherwise.
> + *
> + * DEPRECATED: use device_get_match_data instead, which avoids
> + * common pitfalls due to explicit pointer casts
> + */
>  int dev_get_drvdata(struct device_d *dev, const void **data);
>  
> +/**
> + * device_get_match_data - get driver match data associated with device
> + * @dev: device instance
> + *
> + * Returns match data on success and NULL otherwise
> + */
> +const void *device_get_match_data(struct device_d *dev);
> +
>  int device_match_of_modalias(struct device_d *dev, struct driver_d *drv);
>  
>  #endif /* DRIVER_H */
> -- 
> 2.28.0
> 
> 
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