Re: [PATCH] tty: serdev: fix serdev_device_write return value

Johan Hovold
2017-05-02T09:25:38Z

On Mon, May 01, 2017 at 07:17:14PM -0500, Rob Herring wrote:
> Commit 6fe729c4bdae ("serdev: Add serdev_device_write subroutine")
> provides a compatibility wrapper for the existing
> serdev_device_write_buf, but it fails to return the number of bytes
> written causing users to timeout.

So this would also be fixed for serdev_device_write_buf() by Stefan
Wahren's patch restoring that function implementation, but returning the
amount written is perhaps desirable also for blocking writes for
consistency reasons.

> Fixes: 6fe729c4bdae ("serdev: Add serdev_device_write subroutine")
> Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Rob Herring <robh@kernel.org>
> ---
> drivers/tty/serdev/core.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
> index 433de5ea9b02..ccfe56355c4f 100644
> --- a/drivers/tty/serdev/core.c
> +++ b/drivers/tty/serdev/core.c
> @@ -127,7 +127,7 @@ int serdev_device_write(struct serdev_device *serdev,
> unsigned long timeout)
> {
> struct serdev_controller *ctrl = serdev->ctrl;
> - int ret;
> + int ret, wr_cnt = 0;
>
> if (!ctrl || !ctrl->ops->write_buf ||
> (timeout && !serdev->ops->write_wakeup))
> @@ -143,12 +143,13 @@ int serdev_device_write(struct serdev_device *serdev,
>
> buf += ret;
> count -= ret;
> + wr_cnt += ret;
>
> } while (count &&
> (timeout = wait_for_completion_timeout(&serdev->write_comp,
> timeout)));
>
> mutex_unlock(&serdev->write_lock);
> - return ret < 0 ? ret : (count ? -ETIMEDOUT : 0);
> + return ret < 0 ? ret : (count ? -ETIMEDOUT : wr_cnt);

That's some nasty use of the ternary operator. Ditching it completely
would be more readable.

if (ret < 0)
return ret;

if (count)
return -ETIMEDOUT;

return wr_count;

and here wr_count is the value of count passed to the function (and
could just be stored on entry instead).

> }
> EXPORT_SYMBOL_GPL(serdev_device_write);

Thanks,
Johan