When booting a kernel compiled with CONFIG_CFI_CLANG (kCFI), there is a
CFI failure in ggtt_probe_common() when trying to call hsw_pte_encode()
via an indirect call:

  [    5.030027] CFI failure at ggtt_probe_common+0xd1/0x130 [i915] (target: hsw_pte_encode+0x0/0x30 [i915]; expected type: 0xf5c1d0fc)

With kCFI, indirect calls are validated against their expected type
versus actual type and failures occur when the two types do not match.

clang's -Wincompatible-function-pointer-types-strict can catch this at
compile time but it is not enabled for the kernel yet:

  drivers/gpu/drm/i915/gt/intel_ggtt.c:1155:23: error: incompatible function pointer types assigning to 'u64 (*)(dma_addr_t, unsigned int, u32)' (aka 'unsigned long long (*)(unsigned int, unsigned int, unsigned int)') from 'u64 (dma_addr_t,
  enum i915_cache_level, u32)' (aka 'unsigned long long (unsigned int, enum i915_cache_level, unsigned int)') [-Werror,-Wincompatible-function-pointer-types-strict]
                  ggtt->vm.pte_encode = iris_pte_encode;
                                      ^ ~~~~~~~~~~~~~~~
  drivers/gpu/drm/i915/gt/intel_ggtt.c:1157:23: error: incompatible function pointer types assigning to 'u64 (*)(dma_addr_t, unsigned int, u32)' (aka 'unsigned long long (*)(unsigned int, unsigned int, unsigned int)') from 'u64 (dma_addr_t,
  enum i915_cache_level, u32)' (aka 'unsigned long long (unsigned int, enum i915_cache_level, unsigned int)') [-Werror,-Wincompatible-function-pointer-types-strict]
                  ggtt->vm.pte_encode = hsw_pte_encode;
                                      ^ ~~~~~~~~~~~~~~
  drivers/gpu/drm/i915/gt/intel_ggtt.c:1159:23: error: incompatible function pointer types assigning to 'u64 (*)(dma_addr_t, unsigned int, u32)' (aka 'unsigned long long (*)(unsigned int, unsigned int, unsigned int)') from 'u64 (dma_addr_t,
  enum i915_cache_level, u32)' (aka 'unsigned long long (unsigned int, enum i915_cache_level, unsigned int)') [-Werror,-Wincompatible-function-pointer-types-strict]
                  ggtt->vm.pte_encode = byt_pte_encode;
                                      ^ ~~~~~~~~~~~~~~
  drivers/gpu/drm/i915/gt/intel_ggtt.c:1161:23: error: incompatible function pointer types assigning to 'u64 (*)(dma_addr_t, unsigned int, u32)' (aka 'unsigned long long (*)(unsigned int, unsigned int, unsigned int)') from 'u64 (dma_addr_t,
  enum i915_cache_level, u32)' (aka 'unsigned long long (unsigned int, enum i915_cache_level, unsigned int)') [-Werror,-Wincompatible-function-pointer-types-strict]
                  ggtt->vm.pte_encode = ivb_pte_encode;
                                      ^ ~~~~~~~~~~~~~~
  drivers/gpu/drm/i915/gt/intel_ggtt.c:1163:23: error: incompatible function pointer types assigning to 'u64 (*)(dma_addr_t, unsigned int, u32)' (aka 'unsigned long long (*)(unsigned int, unsigned int, unsigned int)') from 'u64 (dma_addr_t,
  enum i915_cache_level, u32)' (aka 'unsigned long long (unsigned int, enum i915_cache_level, unsigned int)') [-Werror,-Wincompatible-function-pointer-types-strict]
                  ggtt->vm.pte_encode = snb_pte_encode;
                                      ^ ~~~~~~~~~~~~~~
  5 errors generated.

In this case, the pre-gen8 pte_encode functions have a second parameter
type of 'enum i915_cache_level' whereas the function pointer prototype
in 'struct i915_address_space' expects a second parameter type of
'unsigned int'.

Update the second parameter of the callbacks and the comment above them
noting that these statements are still valid, which matches other
functions and files, to clear up the kCFI failures at run time.

Fixes: 9275277d ("drm/i915: use pat_index instead of cache_level")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Fei Yang <fei.yang@intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230530-i915-gt-cache_level-wincompatible-function-pointer-types-strict-v1-1-54501d598229@kernel.org