[PATCH RFC 1/4] i2c: start migrating to a pointer in i2c_device_id

Dmitry Torokhov
2023-08-14T21:54:14Z

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+ kernel_ulong_t driver_data; /* This field is obsolete */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