i2c: designware: Remove i2c_dw_remove_lock_support()

i2c: designware: Remove i2c_dw_remove_lock_support()

When building certain configurations with CONFIG_FINEIBT=y after
commit 894af4a1cde6 ("objtool: Validate kCFI calls"), there is a
warning due to an indirect call in dw_i2c_plat_remove():

  $ cat allno.config
  CONFIG_ACPI=y
  CONFIG_CFI=y
  CONFIG_COMMON_CLK=y
  CONFIG_CPU_MITIGATIONS=y
  CONFIG_I2C=y
  CONFIG_I2C_DESIGNWARE_BAYTRAIL=y
  CONFIG_I2C_DESIGNWARE_CORE=y
  CONFIG_I2C_DESIGNWARE_PLATFORM=y
  CONFIG_IOSF_MBI=y
  CONFIG_MITIGATION_RETPOLINE=y
  CONFIG_MODULES=y
  CONFIG_PCI=y
  CONFIG_X86_KERNEL_IBT=y

  $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 clean allnoconfig vmlinux
  vmlinux.o: warning: objtool: dw_i2c_plat_remove+0x3c: no-cfi indirect call!

With this configuration, i2c_dw_semaphore_cb_table has the BAYTRAIL
member and the sentinel (i.e., 2 members), both of which have an
implicit

  .remove = NULL,

so Clang effectively turns i2c_dw_remove_lock_support(), which is later
inlined into dw_i2c_plat_remove(), into:

  static void i2c_dw_remove_lock_support(struct dw_i2c_dev *dev)
  {
      if (dev->semaphore_idx > 2)
          (*NULL)(dev):
  }

which is not necessarily problematic from a logic perspective (as the
code was not bounds checking semaphore_idx so an out of bounds index
could already crash) but objtool's new __nocfi indirect call checking
trips over Clang dropping the kCFI setup from a known NULL indirect
call.

While it would be possible to fix this by transforming the initial check
into

  if (dev->semaphore_idx < 0 || dev->semaphore_idx >= ARRAY_SIZE(i2c_dw_semaphore_cb_table))

the remove member is unused after commit 440da737cf8d ("i2c: designware:
Use PCI PSP driver for communication"), so i2c_dw_remove_lock_support()
can be removed altogether, as it will never actually do anything.

Closes: https://github.com/ClangBuiltLinux/linux/issues/2133
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20251013-dw_i2c_plat_remove-avoid-objtool-no-cfi-warning-v1-1-8cc4842967bf@kernel.org