On Mon, Sep 28, 2020 at 05:42:41PM +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);
>
> 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
>
> Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
> ---
> 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;
> +}
Can we please give the caller a possibility to distinguish between
errors and a valid NULL pointer?
As you realize in your series some drivers cast the returned value into
an integer type and use 0 as a valid possibility. These need an extra
explanation why we can accept that case. I can think of different
possibilies to get that straight:
- Put a real pointer into matchdata. This is really preferred as it
motivates people to put flags into a (struct type) matchdata which
doesn't lead to excessive if (type == foo || type == bar || type ==
baz) we sometimes see in drivers.
- Return an ERR_PTR from device_get_match_data(). this is less likely
interpreted as a valid int value
- add a int * ret argument to device_get_match_data() which returns
the error code.
Sascha
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