[v2] drm: xlnx: Fix return type of zynqmp_dp_bridge_mode_valid

  From: Nathan Huckleberry <nhuck@google.com>

The mode_valid field in drm_bridge_helper_funcs is expected to be of
type
enum drm_mode_status (* mode_valid) (struct drm_bridge *bridge,
                                     struct drm_display_mode *mode);

The mismatched return type breaks forward edge kCFI since the underlying
function definition does not match the function hook definition. A new
warning in clang will catch this at compile time:

  drivers/gpu/drm/xlnx/zynqmp_dp.c:1573:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' with an expression of type 'int (struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
          .mode_valid = zynqmp_dp_bridge_mode_valid,
                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~
  1 error generated.

The return type of zynqmp_dp_bridge_mode_valid should be changed from
int to enum drm_mode_status.

Reported-by: Dan Carpenter <error27@gmail.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/1703
Link: https://github.com/ClangBuiltLinux/linux/issues/1750
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
[nathan: Rebase on drm-misc-next and fix conflicts
         Add note about new clang warning]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---

Please consider picking this up so that it makes 6.2.

v2:
  - Take over for Nathan, as he is busy with other matters.
  - Rebase on drm-misc-next and resolve conflicts.
  - Add a note about new clang warning that will catch this issue at
    compile time.

v1: https://lore.kernel.org/20220913205600.155172-1-nhuck@google.com/

 drivers/gpu/drm/xlnx/zynqmp_dp.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)


base-commit: 1a0257c352638916fdaffaac2ddedb8e049312f3
  

Hi Nathan,

Thank you for the patch.

On Tue, Nov 08, 2022 at 05:14:25PM -0700, Nathan Chancellor wrote:
> From: Nathan Huckleberry <nhuck@google.com>
> 
> The mode_valid field in drm_bridge_helper_funcs is expected to be of
> type
> enum drm_mode_status (* mode_valid) (struct drm_bridge *bridge,
>                                      struct drm_display_mode *mode);
> 
> The mismatched return type breaks forward edge kCFI since the underlying
> function definition does not match the function hook definition. A new
> warning in clang will catch this at compile time:
> 
>   drivers/gpu/drm/xlnx/zynqmp_dp.c:1573:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' with an expression of type 'int (struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
>           .mode_valid = zynqmp_dp_bridge_mode_valid,
>                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>   1 error generated.
> 
> The return type of zynqmp_dp_bridge_mode_valid should be changed from
> int to enum drm_mode_status.
> 
> Reported-by: Dan Carpenter <error27@gmail.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1703
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Signed-off-by: Nathan Huckleberry <nhuck@google.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> [nathan: Rebase on drm-misc-next and fix conflicts
>          Add note about new clang warning]
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
> 
> Please consider picking this up so that it makes 6.2.

I'll send a pull request shortly.

> v2:
>   - Take over for Nathan, as he is busy with other matters.
>   - Rebase on drm-misc-next and resolve conflicts.
>   - Add a note about new clang warning that will catch this issue at
>     compile time.
> 
> v1: https://lore.kernel.org/20220913205600.155172-1-nhuck@google.com/
> 
>  drivers/gpu/drm/xlnx/zynqmp_dp.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> index 7c9ae167eac7..0a7b466446fb 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> @@ -1362,9 +1362,10 @@ static void zynqmp_dp_bridge_detach(struct drm_bridge *bridge)
>  	zynqmp_dp_aux_cleanup(dp);
>  }
>  
> -static int zynqmp_dp_bridge_mode_valid(struct drm_bridge *bridge,
> -				       const struct drm_display_info *info,
> -				       const struct drm_display_mode *mode)
> +static enum drm_mode_status
> +zynqmp_dp_bridge_mode_valid(struct drm_bridge *bridge,
> +			    const struct drm_display_info *info,
> +			    const struct drm_display_mode *mode)
>  {
>  	struct zynqmp_dp *dp = bridge_to_dp(bridge);
>  	int rate;
> 
> base-commit: 1a0257c352638916fdaffaac2ddedb8e049312f3
  

On Tue, Nov 08, 2022 at 05:14:25PM -0700, Nathan Chancellor wrote:
> From: Nathan Huckleberry <nhuck@google.com>
> 
> The mode_valid field in drm_bridge_helper_funcs is expected to be of
> type
> enum drm_mode_status (* mode_valid) (struct drm_bridge *bridge,
>                                      struct drm_display_mode *mode);
> 
> The mismatched return type breaks forward edge kCFI since the underlying
> function definition does not match the function hook definition. A new
> warning in clang will catch this at compile time:
> 
>   drivers/gpu/drm/xlnx/zynqmp_dp.c:1573:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' with an expression of type 'int (struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
>           .mode_valid = zynqmp_dp_bridge_mode_valid,
>                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>   1 error generated.
> 
> The return type of zynqmp_dp_bridge_mode_valid should be changed from
> int to enum drm_mode_status.
> 
> Reported-by: Dan Carpenter <error27@gmail.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1703
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Signed-off-by: Nathan Huckleberry <nhuck@google.com>

Reviewed-by: Kees Cook <keescook@chromium.org>