[PATCH] serial: mxs-auart: wait for DMA buffer to flush before shutdown

[u.kleine-koenig@pengutronix.de (Uwe Kleine-König)]

Hello Hector,

On Wed, Oct 02, 2013 at 10:09:10AM +0200, Hector Palacios wrote:
> On 10/02/2013 09:44 AM, Uwe Kleine-K?nig wrote:
> >On Wed, Oct 02, 2013 at 09:31:16AM +0200, Hector Palacios wrote:
> >>On 10/01/2013 09:48 PM, Uwe Kleine-K?nig wrote:
> >>>On Tue, Oct 01, 2013 at 06:18:35PM +0200, Hector Palacios wrote:
> >>>>+		/* Wait enough time to flush DMA buffer completely */
> >>>>+		to = u->timeout * UART_XMIT_SIZE / u->fifosize;
> >>>u->timeout is the time needed to send one char, right? UART_XMIT_SIZE is
> >>>the size of the circular buffer, fifosize is the size of the fifo. I
> >>>don't get what you get by dividing by the fifosize. I would have
> >>>expected something like:
> >>>
> >>>	u->timeout * min(UART_XMIT_SIZE, u->fifosize)
> >>>
> >>>Can you explain, maybe in a comment along the code for the next person
> >>>not understanding?
> >>
> >>u->timeout is *not* the time needed to send one char but the time
> >>needed to flush the complete port fifo (see uart_update_timeout() in
> >>serial_core.c where it is set).
> >Ah, right. (BTW, uart_update_timeout should better round up instead of
> >round down, i.e.
> >-	port->timeout = (HZ * bits) / baud + HZ/50;
> >+	port->timeout = DIV_ROUND_UP(HZ * bits, baud) + HZ/50;
> >)
> >
> >>UART_XMIT_SIZE is the number of bytes in the DMA buffer, so I divide
> >>the max number of bytes in the FIFO by the FIFO size and multiply by
> >>the FIFO timeout.
> >ditto here, better round up. Although I think using a completion could
> >shorten the timeout considerably because there are often less than
> >UART_XMIT_SIZE chars in the buffer?!
> 
> I'm not really waiting the full timeout. I'm checking for TX fifo
> empty every 1ms and for a maximum of 'to' ms.
Correct. Still using DIV_ROUND_UP would be better, right?

Best regards
Uwe

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