i2c: designware: Remove i2c_dw_remove_lock_support()

When building certain configurations with CONFIG_FINEIBT=y after
commit 894af4a ("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 440da73 ("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: ClangBuiltLinux#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

Author: nathanchance

drivers/i2c/busses/i2c-designware-core.h

@@ -330,7 +330,6 @@ struct dw_i2c_dev {
 
 struct i2c_dw_semaphore_callbacks {
 	int	(*probe)(struct dw_i2c_dev *dev);
-	void	(*remove)(struct dw_i2c_dev *dev);
 };
 
 int i2c_dw_init_regmap(struct dw_i2c_dev *dev);

drivers/i2c/busses/i2c-designware-platdrv.c

@@ -197,15 +197,6 @@ static int i2c_dw_probe_lock_support(struct dw_i2c_dev *dev)
 	return 0;
 }
 
-static void i2c_dw_remove_lock_support(struct dw_i2c_dev *dev)
-{
-	if (dev->semaphore_idx < 0)
-		return;
-
-	if (i2c_dw_semaphore_cb_table[dev->semaphore_idx].remove)
-		i2c_dw_semaphore_cb_table[dev->semaphore_idx].remove(dev);
-}
-
 static int dw_i2c_plat_probe(struct platform_device *pdev)
 {
 	u32 flags = (uintptr_t)device_get_match_data(&pdev->dev);
@@ -339,8 +330,6 @@ static void dw_i2c_plat_remove(struct platform_device *pdev)
 
 	i2c_dw_prepare_clk(dev, false);
 
-	i2c_dw_remove_lock_support(dev);
-
 	reset_control_assert(dev->rst);
 }