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From:   Nathan Chancellor <nathan@kernel.org>
To:     Hyun Kwon <hyun.kwon@xilinx.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, Kees Cook <keescook@chromium.org>,
        Sami Tolvanen <samitolvanen@google.com>, llvm@lists.linux.dev,
        linux-kernel@vger.kernel.org, patches@lists.linux.dev,
        Nathan Huckleberry <nhuck@google.com>,
        Dan Carpenter <error27@gmail.com>,
        Nathan Chancellor <nathan@kernel.org>
Subject: [PATCH v2] drm: xlnx: Fix return type of zynqmp_dp_bridge_mode_valid
Date:   Tue,  8 Nov 2022 17:14:25 -0700
Message-Id: <20221109001424.1422495-1-nathan@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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(-)

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
-- 
2.38.1