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SubjectRe: [PATCH] misc: hmc6352: fix wrong return value checking for i2c_master_recv
On Wed, 09 Mar 2011 16:41:56 +0800
Axel Lin <axel.lin@gmail.com> wrote:

> i2c_master_recv() returns negative errno, or else the number of bytes read.
> Thus i2c_master_recv(client, i2c_data, 2) returns 2 instead of 1 in success case.
>
> Signed-off-by: Axel Lin <axel.lin@gmail.com>
> ---
> drivers/misc/hmc6352.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/misc/hmc6352.c b/drivers/misc/hmc6352.c
> index 234bfca..3afc11e 100644
> --- a/drivers/misc/hmc6352.c
> +++ b/drivers/misc/hmc6352.c
> @@ -86,7 +86,7 @@ static ssize_t compass_heading_data_show(struct device *dev,
> msleep(10); /* sending 'A' cmd we need to wait for 7-10 millisecs */
> ret = i2c_master_recv(client, i2c_data, 2);
> mutex_unlock(&compass_mutex);
> - if (ret != 1) {
> + if (ret < 0) {
> dev_warn(dev, "i2c read data cmd failed\n");
> return ret;
> }

The problem seems real but the fix won't work:

--- a/drivers/misc/hmc6352.c~drivers-misc-hmc6352c-fix-wrong-return-value-checking-for-i2c_master_recv-fix
+++ a/drivers/misc/hmc6352.c
@@ -75,7 +75,7 @@ static ssize_t compass_heading_data_show
{
struct i2c_client *client = to_i2c_client(dev);
unsigned char i2c_data[2];
- unsigned int ret;
+ int ret;

mutex_lock(&compass_mutex);
ret = compass_command(client, 'A');


I also wonder if this bit is correct:

: static ssize_t compass_heading_data_show(struct device *dev,
: struct device_attribute *attr, char *buf)
: {
: struct i2c_client *client = to_i2c_client(dev);
: unsigned char i2c_data[2];
: int ret;
:
: mutex_lock(&compass_mutex);
: ret = compass_command(client, 'A');
: if (ret != 1) {
: mutex_unlock(&compass_mutex);
: return ret;
: }

If compass_command() returns zero (short write on i2c?!?!?) then did we
do the right thing?



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