Hi Jacopo
On Mon, 20 Feb 2023 at 12:41, Jacopo Mondi
<jacopo.mondi@xxxxxxxxxxxxxxxx> wrote:
>
> The ov5647_read() functions calls i2c_master_send() and
> i2c_master_read() in sequence. However this leaves space for other
> clients to contend the bus and insert a unrelated transaction in between
> the two calls.
>
> Replace the two calls with a single i2c_transfer() one, that locks the
> bus in between the transactions.
>
> Signed-off-by: Jacopo Mondi <jacopo.mondi@xxxxxxxxxxxxxxxx>
> ---
> drivers/media/i2c/ov5647.c | 24 +++++++++++++++---------
> 1 file changed, 15 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/media/i2c/ov5647.c b/drivers/media/i2c/ov5647.c
> index 0b88ac6dee41..a423ee8fe20c 100644
> --- a/drivers/media/i2c/ov5647.c
> +++ b/drivers/media/i2c/ov5647.c
> @@ -631,23 +631,29 @@ static int ov5647_write(struct v4l2_subdev *sd, u16 reg, u8 val)
>
> static int ov5647_read(struct v4l2_subdev *sd, u16 reg, u8 *val)
> {
> - unsigned char data_w[2] = { reg >> 8, reg & 0xff };
> struct i2c_client *client = v4l2_get_subdevdata(sd);
> + u8 buf[2] = { reg >> 8, reg & 0xff };
> + struct i2c_msg msg[2];
> int ret;
>
> - ret = i2c_master_send(client, data_w, 2);
> + msg[0].addr = client->addr;
> + msg[0].flags = client->flags;
> + msg[0].buf = buf;
> + msg[0].len = sizeof(buf);
> +
> + msg[1].addr = client->addr;
> + msg[1].flags = client->flags | I2C_M_RD;
> + msg[1].buf = buf;
> + msg[1].len = 1;
> +
> + ret = i2c_transfer(client->adapter, msg, 2);
> if (ret < 0) {
i2c_transfer
* Returns negative errno, else the number of messages executed.
Is there a valid failure case where it returns 1 having done the write
but failed the read? It's deferred to the individual I2C driver, so
could quite easily be iffy.
Personally I'd be tempted to check if (ret != 2), and remap any other
positive value to -EINVAL.
Otherwise:
Reviewed-by: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx>
> - dev_dbg(&client->dev, "%s: i2c write error, reg: %x\n",
> + dev_err(&client->dev, "%s: i2c read error, reg: %x\n",
> __func__, reg);
> return ret;
> }
>
> - ret = i2c_master_recv(client, val, 1);
> - if (ret < 0) {
> - dev_dbg(&client->dev, "%s: i2c read error, reg: %x\n",
> - __func__, reg);
> - return ret;
> - }
> + *val = buf[0];
>
> return 0;
> }
> --
> 2.39.0
>
