From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Subject: Re: [PATCH] serial: mxs-auart: wait for DMA buffer to flush before shutdown Date: Wed, 2 Oct 2013 10:30:14 +0200 Message-ID: <20131002083014.GN2548@pengutronix.de> References: <1380644315-31581-1-git-send-email-hector.palacios@digi.com> <20131001194800.GL2548@pengutronix.de> <524BCBC4.5050708@digi.com> <20131002074436.GM2548@pengutronix.de> <524BD4A6.5060208@digi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from metis.ext.pengutronix.de ([92.198.50.35]:50635 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753188Ab3JBIaX (ORCPT ); Wed, 2 Oct 2013 04:30:23 -0400 Content-Disposition: inline In-Reply-To: <524BD4A6.5060208@digi.com> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Hector Palacios Cc: "fabio.estevam@freescale.com" , "marex@denx.de" , "gregkh@linuxfoundation.org" , "b32955@freescale.com" , "linux-serial@vger.kernel.org" , "shawn.guo@linaro.org" , Jiri Slaby , "linux-arm-kernel@lists.infradead.org" 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=F6nig wrote: > >On Wed, Oct 02, 2013 at 09:31:16AM +0200, Hector Palacios wrote: > >>On 10/01/2013 09:48 PM, Uwe Kleine-K=F6nig wrote: > >>>On Tue, Oct 01, 2013 at 06:18:35PM +0200, Hector Palacios wrote: > >>>>+ /* Wait enough time to flush DMA buffer completely */ > >>>>+ to =3D u->timeout * UART_XMIT_SIZE / u->fifosize; > >>>u->timeout is the time needed to send one char, right? UART_XMIT_S= IZE 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 pe= rson > >>>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() i= n > >>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 =3D (HZ * bits) / baud + HZ/50; > >+ port->timeout =3D DIV_ROUND_UP(HZ * bits, baud) + HZ/50; > >) > > > >>UART_XMIT_SIZE is the number of bytes in the DMA buffer, so I divid= e > >>the max number of bytes in the FIFO by the FIFO size and multiply b= y > >>the FIFO timeout. > >ditto here, better round up. Although I think using a completion cou= ld > >shorten the timeout considerably because there are often less than > >UART_XMIT_SIZE chars in the buffer?! >=20 > 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 --=20 Pengutronix e.K. | Uwe Kleine-K=F6nig = | Industrial Linux Solutions | http://www.pengutronix.de/= | -- To unsubscribe from this list: send the line "unsubscribe linux-serial"= in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html