Hi,
This series removes the redundant driver field from the i2c_client struct. The field is redundant since the same pointer can be accessed through to_i2c_driver(client->dev.driver). The commit log suggests that the field has been around since forever (since before v2.6.12-rc2) and it looks as if it was simply forgotten to remove it during the conversion of the i2c framework to the generic device driver model.
Nevertheless there are a still a few users of the field around. This series first updates all users to use an alternative method of accessing the same data and then the last patch removes the driver field from the i2c_client struct.
Note that due to this changes on most architectures neither the code size nor the type of generated instructions will change. This is due to the fact that we aren't really interested in the pointer value itself, but rather want to dereference it to access one of the fields of the struct. offset_of() (and hence to_i2c_driver) works by subtracting a offset from the pointer, so the compiler can internally create the sum of these two offsets and use that to access the field.
E.g. on ARM the expression client->driver->command(...) generates
... ldr r3, [r0, #28] ldr r3, [r3, #32] blx r3 ...
and the expression to_i2c_driver(client->dev.driver)->command(...) generates
... ldr r3, [r0, #160] ldr r3, [r3, #-4] blx r3 ...
Other architectures will generate similar code.
The most common pattern is to use the i2c_driver to get to the device_driver struct embedded in it. The same struct can easily be accessed through the device struct embedded in the i2c_client struct. E.g. client->driver->driver.field can be replaced by client->dev.driver->field. Here again the generated code is almost identical and only the offsets differ.
E.g. on ARM the expression 'client->driver->driver.owner' generates
ldr r3, [r0, #28] ldr r0, [r3, #44]
and 'client->dev.driver->owner' generates
ldr r3, [r0, #160] ldr r0, [r3, #8]
The kernel overall code size is slightly reduced since the code that manages the driver field is removed and of course also the runtime memory footprint of the i2c_client struct is reduced.
- Lars
Lars-Peter Clausen (8): [media] s5c73m3: Don't use i2c_client->driver [media] exynos4-is: Don't use i2c_client->driver [media] core: Don't use i2c_client->driver drm: encoder_slave: Don't use i2c_client->driver drm: nouveau: Don't use i2c_client->driver ALSA: ppc: keywest: Don't use i2c_client->driver ASoC: imx-wm8962: Don't use i2c_client->driver i2c: Remove redundant 'driver' field from the i2c_client struct
drivers/gpu/drm/drm_encoder_slave.c | 8 ++++---- drivers/gpu/drm/nouveau/core/subdev/therm/ic.c | 3 ++- drivers/i2c/i2c-core.c | 21 ++++++++++++--------- drivers/i2c/i2c-smbus.c | 10 ++++++---- drivers/media/i2c/s5c73m3/s5c73m3-core.c | 2 +- drivers/media/platform/exynos4-is/media-dev.c | 6 +++--- drivers/media/v4l2-core/tuner-core.c | 6 +++--- drivers/media/v4l2-core/v4l2-common.c | 10 +++++----- include/linux/i2c.h | 2 -- include/media/v4l2-common.h | 2 +- sound/ppc/keywest.c | 4 ++-- sound/soc/fsl/imx-wm8962.c | 2 +- 12 files changed, 40 insertions(+), 36 deletions(-)