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    Subject[PATCH RFC 1/4] i2c: start migrating to a pointer in i2c_device_id
    Date
    The of_device_id structure uses a void pointer to associate additional
    driver-private data with device id, most commonly used to refer to a
    structure containing additional characteristics of a particular chip.
    However i2c_device_id uses an unsigned long. While it can easily be
    converted to a pointer, several drivers use it to store a scalar (and it
    is possible to use a pointer in of_device_id to store a scalar value as
    well). The worst case comes when OF part of a driver uses pointers,
    while legacy part is using scalars, causing constructs like:

    data = device_get_match_data(...);
    if (!data)
    data = &some_array[i2c_match_id(...)->data];
    ...

    To avoid this introduce a const void "data" pointer to i2c_device_id as
    well, so that we can convert drivers one by one, and drop driver_data
    member in the end.

    The end goal is to clean up all helpers and make device_get_match_data()
    work universally for all ACPI, DT, and legacy variants.

    Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
    ---
    drivers/i2c/i2c-core-base.c | 2 +-
    include/linux/mod_devicetable.h | 3 ++-
    2 files changed, 3 insertions(+), 2 deletions(-)

    diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
    index 60746652fd52..75d12d79d8f1 100644
    --- a/drivers/i2c/i2c-core-base.c
    +++ b/drivers/i2c/i2c-core-base.c
    @@ -126,7 +126,7 @@ const void *i2c_get_match_data(const struct i2c_client *client)
    if (!match)
    return NULL;

    - data = (const void *)match->driver_data;
    + data = match->data ?: (const void *)match->driver_data;
    }

    return data;
    diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
    index b0678b093cb2..21ac2a96e828 100644
    --- a/include/linux/mod_devicetable.h
    +++ b/include/linux/mod_devicetable.h
    @@ -477,7 +477,8 @@ struct rpmsg_device_id {

    struct i2c_device_id {
    char name[I2C_NAME_SIZE];
    - kernel_ulong_t driver_data; /* Data private to the driver */
    + kernel_ulong_t driver_data; /* This field is obsolete */
    + const void *data; /* Data private to the driver */
    };

    /* pci_epf */
    --
    2.41.0.694.ge786442a9b-goog

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