linux-kernel - [PATCH] drm/i915/display: Ensure that ret is always initialized in icl_combo_phy_verify

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Date:   Wed, 15 Jul 2020 21:27:42 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc:     José Roberto de Souza <jose.souza@...el.com>,
        Matt Roper <matthew.d.roper@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] drm/i915/display: Ensure that ret is always initialized in icl_combo_phy_verify_state

Clang warns:

drivers/gpu/drm/i915/display/intel_combo_phy.c:268:3: warning: variable
'ret' is uninitialized when used here [-Wuninitialized]
                ret &= check_phy_reg(dev_priv, phy, ICL_PORT_TX_DW8_LN0(phy),
                ^~~
drivers/gpu/drm/i915/display/intel_combo_phy.c:261:10: note: initialize
the variable 'ret' to silence this warning
        bool ret;
                ^
                 = 0
1 warning generated.

In practice, the bug this warning appears to be concerned with would not
actually matter because ret gets initialized to the return value of
cnl_verify_procmon_ref_values. However, that does appear to be a bug
since it means the first hunk of the patch this fixes won't actually do
anything (since the values of check_phy_reg won't factor into the final
ret value). Initialize ret to true then make all of the assignments a
bitwise AND with itself so that the function always does what it should
do.

Fixes: 239bef676d8e ("drm/i915/display: Implement new combo phy initialization step")
Link: https://github.com/ClangBuiltLinux/linux/issues/1094
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---
 drivers/gpu/drm/i915/display/intel_combo_phy.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_combo_phy.c b/drivers/gpu/drm/i915/display/intel_combo_phy.c
index eccaa79cb4a9..a4b8aa6d0a9e 100644
--- a/drivers/gpu/drm/i915/display/intel_combo_phy.c
+++ b/drivers/gpu/drm/i915/display/intel_combo_phy.c
@@ -258,7 +258,7 @@ static bool phy_is_master(struct drm_i915_private *dev_priv, enum phy phy)
 static bool icl_combo_phy_verify_state(struct drm_i915_private *dev_priv,
 				       enum phy phy)
 {
-	bool ret;
+	bool ret = true;
 	u32 expected_val = 0;
 
 	if (!icl_combo_phy_enabled(dev_priv, phy))
@@ -276,7 +276,7 @@ static bool icl_combo_phy_verify_state(struct drm_i915_private *dev_priv,
 				     DCC_MODE_SELECT_CONTINUOSLY);
 	}
 
-	ret = cnl_verify_procmon_ref_values(dev_priv, phy);
+	ret &= cnl_verify_procmon_ref_values(dev_priv, phy);
 
 	if (phy_is_master(dev_priv, phy)) {
 		ret &= check_phy_reg(dev_priv, phy, ICL_PORT_COMP_DW8(phy),

base-commit: ca0e494af5edb59002665bf12871e94b4163a257
-- 
2.28.0.rc0