linux-kernel - Re: [PATCH] tty: serdev: fix serdev_device

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Date:   Tue, 2 May 2017 11:25:27 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrey Smirnov <andrew.smirnov@...il.com>
Subject: Re: [PATCH] tty: serdev: fix serdev_device_write return value

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@...il.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Rob Herring <robh@...nel.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