linux-kernel - [PATCH 3.16 012/132] media: davinci-isif: avoid uninitialized variable use

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Date:   Fri, 20 Sep 2019 15:23:35 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Hans Verkuil" <hverkuil-cisco@...all.nl>,
        "Nathan Chancellor" <natechancellor@...il.com>,
        "Arnd Bergmann" <arnd@...db.de>,
        "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
        "Mauro Carvalho Chehab" <mchehab+samsung@...nel.org>
Subject: [PATCH 3.16 012/132] media: davinci-isif: avoid uninitialized
 variable use

3.16.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Arnd Bergmann <arnd@...db.de>

commit 0e633f97162c1c74c68e2eb20bbd9259dce87cd9 upstream.

clang warns about a possible variable use that gcc never
complained about:

drivers/media/platform/davinci/isif.c:982:32: error: variable 'frame_size' is uninitialized when used here
      [-Werror,-Wuninitialized]
                dm365_vpss_set_pg_frame_size(frame_size);
                                             ^~~~~~~~~~
drivers/media/platform/davinci/isif.c:887:2: note: variable 'frame_size' is declared here
        struct vpss_pg_frame_size frame_size;
        ^
1 error generated.

There is no initialization for this variable at all, and there
has never been one in the mainline kernel, so we really should
not put that stack data into an mmio register.

On the other hand, I suspect that gcc checks the condition
more closely and notices that the global
isif_cfg.bayer.config_params.test_pat_gen flag is initialized
to zero and never written to from any code path, so anything
depending on it can be eliminated.

To shut up the clang warning, just remove the dead code manually,
it has probably never been used because any attempt to do so
would have resulted in undefined behavior.

Fixes: 63e3ab142fa3 ("V4L/DVB: V4L - vpfe capture - source for ISIF driver on DM365")

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Acked-by: Lad, Prabhakar <prabhakar.csengg@...il.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@...all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/media/platform/davinci/isif.c | 9 ---------
 1 file changed, 9 deletions(-)

--- a/drivers/media/platform/davinci/isif.c
+++ b/drivers/media/platform/davinci/isif.c
@@ -890,9 +890,7 @@ static int isif_set_hw_if_params(struct
 static int isif_config_ycbcr(void)
 {
 	struct isif_ycbcr_config *params = &isif_cfg.ycbcr;
-	struct vpss_pg_frame_size frame_size;
 	u32 modeset = 0, ccdcfg = 0;
-	struct vpss_sync_pol sync;
 
 	dev_dbg(isif_cfg.dev, "\nStarting isif_config_ycbcr...");
 
@@ -980,13 +978,6 @@ static int isif_config_ycbcr(void)
 		/* two fields are interleaved in memory */
 		regw(0x00000249, SDOFST);
 
-	/* Setup test pattern if enabled */
-	if (isif_cfg.bayer.config_params.test_pat_gen) {
-		sync.ccdpg_hdpol = params->hd_pol;
-		sync.ccdpg_vdpol = params->vd_pol;
-		dm365_vpss_set_sync_pol(sync);
-		dm365_vpss_set_pg_frame_size(frame_size);
-	}
 	return 0;
 }