Added spi mailing list (+ likely interested people) as the same approach is used for device registration as with i2c. > Dear All, > > Within board configuration files, i2c devices are currently allocated using > i2c_board_info structures. The only element of these that retains it's > memory address once the struct device elements are allocated (upon adapter > initialization) is the platform data pointer. > > Several subsystems (regulator and clock for example) use an association > method based upon a device specific string associated with a pointer to > a device structure. Unfortunately as things currently stand there is no > means of obtaining a suitable device for i2c devices at the point when > it is required (in the board config). > > So the question is, how to overcome this problem? > > Options that I can come up with are: > > 1) Relax the constraints that the token used for device identification > in subsystems using the regulators approach to a void * and use > the platform data pointer of an i2c device. Note this requires > every device which may need a regulator to have platform data. > Whilst this would work, it is far from ideal. As Mark Brown pointed out: This would also remove the ability of the APIs using this to use the struct device for other things like showing what they're doing in sysfs or use dev_printk. > > 2) Allow more static allocation of struct i2c_client. The way of doing > this with minimal disruption would be to add a pointer to i2c_board_info > to a preallocated i2c_client structure and if this is supplied do not > allocate another. A flag can then be used to indicated whether the > structure has been statically allocated or not (thus preventing it > being inadvertently freed. > > 3) Allow static allocation of i2c_client structures as a direct alternative > to having any i2c_board_info structures at all. As the majority if not > all of i2c_board_info's elements are simply copied into the i2c_client > structure anyway, there is considerable overhead in option 2. Clearly > it would not be simple or necessarily advisable to remove i2c_board_info > structures so I would propose providing an alternative set of registration > functions which would only be used when people cared about the problem > we are addressing here. > > What do people think? In particular can anyone come up with any other / > better way round this issue. (or am I missing something?) > In particular, are there any similar cases already in kernel that would > suggest a particular approach to solving this issue? > > I have an implementation of option 2 that works fine and is relatively simple. > > Thanks, > > --- > Jonathan Cameron > -- > To unsubscribe from this list: send the line "unsubscribe linux-i2c" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
