counter: Internalize sysfs interface code
This is a reimplementation of the Generic Counter driver interface. There are no modifications to the Counter subsystem userspace interface, so existing userspace applications should continue to run seamlessly. The purpose of this patch is to internalize the sysfs interface code among the various counter drivers into a shared module. Counter drivers pass and take data natively (i.e. u8, u64, etc.) and the shared counter module handles the translation between the sysfs interface and the device drivers. This guarantees a standard userspace interface for all counter drivers, and helps generalize the Generic Counter driver ABI in order to support the Generic Counter chrdev interface (introduced in a subsequent patch) without significant changes to the existing counter drivers. Note, Counter device registration is the same as before: drivers populate a struct counter_device with components and callbacks, then pass the structure to the devm_counter_register function. However, what's different now is how the Counter subsystem code handles this registration internally. Whereas before callbacks would interact directly with sysfs data, this interaction is now abstracted and instead callbacks interact with native C data types. The counter_comp structure forms the basis for Counter extensions. The counter-sysfs.c file contains the code to parse through the counter_device structure and register the requested components and extensions. Attributes are created and populated based on type, with respective translation functions to handle the mapping between sysfs and the counter driver callbacks. The translation performed for each attribute is straightforward: the attribute type and data is parsed from the counter_attribute structure, the respective counter driver read/write callback is called, and sysfs I/O is handled before or after the driver read/write function is called. Cc: Jarkko Nikula <jarkko.nikula@linux.intel.com> Cc: Patrick Havelange <patrick.havelange@essensium.com> Cc: Kamel Bouhara <kamel.bouhara@bootlin.com> Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com> Cc: Alexandre Torgue <alexandre.torgue@st.com> Cc: Dan Carpenter <dan.carpenter@oracle.com> Acked-by:Syed Nayyar Waris <syednwaris@gmail.com> Reviewed-by:
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