linux-kernel - Re: [PATCH v2] USB: serial: cp210x: Add tx

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Date:	Thu, 26 Nov 2015 08:35:12 +0100
From:	Johan Hovold <johan@...nel.org>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>,
	johan@...nel.org, USB <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] USB: serial: cp210x: Add tx_empty()

On Wed, Nov 25, 2015 at 10:26:12PM +0200, Andy Shevchenko wrote:
> On Wed, Nov 25, 2015 at 12:28 AM, Konstantin Shkolnyy
> <konstantin.shkolnyy@...il.com> wrote:
> > Added tx_empty callback needed for generic wait-until-sent support.
> > Without this function, when the port is closed usbserial can't know that
> > there are still data in the chip's transmit FIFO. The chip gets disabled
> > and untransmitted data lost. When the actual byte count is reported by
> > tx-empty the close can be delayed until all data are sent.
> >
> 
> >  /*
> > + * Read how many bytes are waiting in the TX queue.
> > + */
> 
> One line?

Not necessarily for a function header.

> > +static bool cp210x_tx_empty(struct usb_serial_port *port)
> > +{
> > +       int err;
> > +       u32 count;
> > +
> > +       err = cp210x_get_tx_queue_byte_count(port, &count);
> 
> > +       if (!err && count)
> > +               return false;
> > +
> > +       return true;
> 
> return err || !count;

Nah, I don't consider that an improvement.

I prefer separating the error and success paths, for example:

	if (err)
		return true;

	return !count;

but the current code is also ok.

> Btw, can be count left uninitialized?

Yes, but that's not an issue. Clearly separating the success and errors
paths as I suggested above would make that more obvious however.

I'll fix that up before applying.

Thanks,
Johan
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