usb: xhci: standardize multi bit-field macros

This patch aims to unify the format of register macros and masks within
the xHCI driver. Currently, register macros have inconsistent bit-field
masks, get macros, and set macros, with varying naming conventions and
functionalities.

==================== Proposal ====================
* Introduce a standardized approach by using only mask macros for each bit
  field, leveraging GENMASK() for enhanced clarity.

  #define HCC_MAX_PSA		GENMASK(15, 12)

* Utilize FIELD_GET() and FIELD_PREP() macros directly in the C code for
  getting and setting values, ensuring consistency and readability.

  u32 psa = FIELD_GET(HCC_MAX_PSA, reg);

* Maintain exceptions for macros that perform custom operations.

  #define CTX_SIZE(_hcc)	(_hcc & HCC_64BYTE_CONTEXT ? 64 : 32)

* Note, while FIELD_*() macros are beneficial, I am not suggesting that
  they should always be used. Instead, use them where they simplify the
  code and eliminate the necessity for custom get/set macros.
  In the example below, additional FIELD_PREP() or FIELD_MODIFY() is not
  beneficial.

  #define HCS_MAX_SCRATCHPAD(p)   (FIELD_GET(HCS_MAX_SP_HI, (p)) << 5 | \
				   FIELD_GET(HCS_MAX_SP_LO, (p)))

==================== Improvements ====================
Simplified Macros:
  By reducing custom macros, the code becomes more straightforward.
  Macros FIELD_GET() and FIELD_PREP() are commonly used, which contributes
  to the code readability and consistency.

  $ git grep -n 'FIELD_GET' | wc -l
  9027
  $ git grep -n 'FIELD_PREP' | wc -l
  15407

Consistent Return Type:
  All bit macros will return unsigned 64-bit values, mitigating potential
  cross-architecture issues.

Unified Bit Range Definition:
  The mask macro will define bit ranges, eliminating separate definitions
  for get/set macros. Because, FIELD_GET() & FIELD_PREP() use mask macro.

Cleaner header file with less macros:
  Fewer macros result in a cleaner and more manageable header file.

Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://patch.msgid.link/20260806142113.2436238-12-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions