linux-kernel - [PATCH v1 2/8] media: ov2740: Replace voodoo coding with understandle flow

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Date:   Tue, 26 Jul 2022 15:05:50 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Tianshu Qiu <tian.shu.qiu@...el.com>,
        Shawn Tu <shawnx.tu@...el.com>,
        Bingbu Cao <bingbu.cao@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Subject: [PATCH v1 2/8] media: ov2740: Replace voodoo coding with understandle flow

Besides not being understandable at the first glance, the code
might provoke a compiler or a static analyser tool to warn about
out-of-bound access (when len == 0).

Replace it with clear flow an understandable intention.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 drivers/media/i2c/ov2740.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/drivers/media/i2c/ov2740.c b/drivers/media/i2c/ov2740.c
index c975db1bbe8c..81c0ab220339 100644
--- a/drivers/media/i2c/ov2740.c
+++ b/drivers/media/i2c/ov2740.c
@@ -377,10 +377,10 @@ static int ov2740_read_reg(struct ov2740 *ov2740, u16 reg, u16 len, u32 *val)
 	struct i2c_client *client = v4l2_get_subdevdata(&ov2740->sd);
 	struct i2c_msg msgs[2];
 	u8 addr_buf[2];
-	u8 data_buf[4] = {0};
+	u8 data_buf[4];
 	int ret = 0;
 
-	if (len > sizeof(data_buf))
+	if (len > 4)
 		return -EINVAL;
 
 	put_unaligned_be16(reg, addr_buf);
@@ -391,13 +391,22 @@ static int ov2740_read_reg(struct ov2740 *ov2740, u16 reg, u16 len, u32 *val)
 	msgs[1].addr = client->addr;
 	msgs[1].flags = I2C_M_RD;
 	msgs[1].len = len;
-	msgs[1].buf = &data_buf[sizeof(data_buf) - len];
+	msgs[1].buf = data_buf;
 
 	ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
 	if (ret != ARRAY_SIZE(msgs))
 		return ret < 0 ? ret : -EIO;
 
-	*val = get_unaligned_be32(data_buf);
+	if (len == 4)
+		*val = get_unaligned_be32(data_buf);
+	else if (len == 3)
+		*val = get_unaligned_be24(data_buf);
+	else if (len == 2)
+		*val = get_unaligned_be16(data_buf);
+	else if (len == 1)
+		*val = data_buf[0];
+	else
+		return -EINVAL;
 
 	return 0;
 }
@@ -412,7 +421,16 @@ static int ov2740_write_reg(struct ov2740 *ov2740, u16 reg, u16 len, u32 val)
 		return -EINVAL;
 
 	put_unaligned_be16(reg, buf);
-	put_unaligned_be32(val << 8 * (4 - len), buf + 2);
+	if (len == 4)
+		put_unaligned_be32(val, buf + 2);
+	else if (len == 3)
+		put_unaligned_be24(val, buf + 2);
+	else if (len == 2)
+		put_unaligned_be16(val, buf + 2);
+	else if (len == 1)
+		buf[2] = val;
+	else
+		return -EINVAL;
 
 	ret = i2c_master_send(client, buf, len + 2);
 	if (ret != len + 2)
-- 
2.35.1