linux-kernel - [PATCH] drm/amd/powerplay: Zero initialize num_of_levels in vega20_set_single_dpm

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Date:   Tue, 19 Mar 2019 17:58:42 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Rex Zhu <rex.zhu@....com>, Evan Quan <evan.quan@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] drm/amd/powerplay: Zero initialize num_of_levels in vega20_set_single_dpm_table

When building with -Wsometimes-uninitialized, Clang warns:

drivers/gpu/drm/amd/amdgpu/../powerplay/vega20_ppt.c:456:2: warning:
variable 'num_of_levels' is used uninitialized whenever '?:' condition
is false [-Wsometimes-uninitialized]
        smu_read_smc_arg(smu, &num_of_levels);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../powerplay/inc/amdgpu_smu.h:608:3: note:
expanded from macro 'smu_read_smc_arg'
        ((smu)->funcs->read_smc_arg? (smu)->funcs->read_smc_arg((smu), (arg)) : 0)
         ^~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../powerplay/vega20_ppt.c:457:7: note:
uninitialized use occurs here
        if (!num_of_levels) {
             ^~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../powerplay/vega20_ppt.c:456:2: note: remove
the '?:' if its condition is always true
        smu_read_smc_arg(smu, &num_of_levels);
        ^
drivers/gpu/drm/amd/amdgpu/../powerplay/inc/amdgpu_smu.h:608:3: note:
expanded from macro 'smu_read_smc_arg'
        ((smu)->funcs->read_smc_arg? (smu)->funcs->read_smc_arg((smu), (arg)) : 0)
         ^
drivers/gpu/drm/amd/amdgpu/../powerplay/vega20_ppt.c:446:27: note:
initialize the variable 'num_of_levels' to silence this warning
        uint32_t i, num_of_levels, clk;
                                 ^
                                  = 0
1 warning generated.

The if statement it mentions as potentially problematic is currently
always true because the read_smc_arg callback is assigned at the
bottom of this file but Clang can't tell that. If the callback were
ever to disappear, num_of_levels would never be initialized. Just
zero initialize it to ensure that the intent behind this code
remains the same.

Fixes: 870b996f955f ("drm/amd/powerplay: set defalut dpm table for smu")
Link: https://github.com/ClangBuiltLinux/linux/issues/425
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---
 drivers/gpu/drm/amd/powerplay/vega20_ppt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/powerplay/vega20_ppt.c b/drivers/gpu/drm/amd/powerplay/vega20_ppt.c
index 7e9e8ad9a300..41e6f49c9cb6 100644
--- a/drivers/gpu/drm/amd/powerplay/vega20_ppt.c
+++ b/drivers/gpu/drm/amd/powerplay/vega20_ppt.c
@@ -443,7 +443,7 @@ vega20_set_single_dpm_table(struct smu_context *smu,
 			    PPCLK_e clk_id)
 {
 	int ret = 0;
-	uint32_t i, num_of_levels, clk;
+	uint32_t i, num_of_levels = 0, clk;
 
 	ret = smu_send_smc_msg_with_param(smu,
 			SMU_MSG_GetDpmFreqByIndex,
-- 
2.21.0