From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfram Sang Subject: Re: [PATCH] serial imx.c: fix CTS trigger level lower to avoid lost chars Date: Fri, 22 Jan 2010 12:49:35 +0100 Message-ID: <20100122114934.GE4782@pengutronix.de> References: <1264109163-28739-1-git-send-email-valentin.longchamp@epfl.ch> <20100121220653.GA21010@pengutronix.de> <20100121221133.GA30419@n2100.arm.linux.org.uk> <4B597A82.4020906@epfl.ch> <20100122110701.GA15699@shareable.org> <20100122113130.GB10449@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="2qXFWqzzG3v1+95a" Return-path: Received: from metis.ext.pengutronix.de ([92.198.50.35]:47309 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754857Ab0AVLtk (ORCPT ); Fri, 22 Jan 2010 06:49:40 -0500 Content-Disposition: inline In-Reply-To: <20100122113130.GB10449@n2100.arm.linux.org.uk> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Russell King - ARM Linux Cc: Jamie Lokier , "s.hauer@pengutronix.de" , "linux-serial@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Valentin Longchamp --2qXFWqzzG3v1+95a Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable > What you're assuming is that flow control was there to prevent overruns > on the hardware receiver. That's not the way it works on these devices; > flow control is entirely managed in software - there is no hardware > assistance. >=20 > The flow control implemented for non-FIFO and non-hardware assisted > UARTs is purely to do with preventing the software buffer behind the > UART from overflowing - it can't prevent the device's receiver buffering > from overrunning. (Non-FIFO devices have the shift register and a > buffer register - complete reception of a second character before the > first is read causes an overrun condition.) >=20 > If you have overruns on the receiver, that's an interrupt latency > problem and its an error that's reported to the receiver side only. >=20 > Yes, later devices have the ability in hardware to deassert RTS when > the receiver FIFO gets above a certain threshold to /help/ prevent > overruns occuring when there's high interrupt latency - but normal > system operation should still ensure that the FIFO is emptied in a > timely manner. >=20 > They also gained the ability to stop the transmitter once CTS is > deasserted, mainly because the transmitter FIFOs in these devices > is soo large (maybe 32 to 128 bytes deep.) Russell, thanks for this explanation. Patch seems principally OK to me, the= n. Regards, Wolfram --=20 Pengutronix e.K. | Wolfram Sang | Industrial Linux Solutions | http://www.pengutronix.de/ | --2qXFWqzzG3v1+95a Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAktZkM4ACgkQD27XaX1/VRsLpwCfWd2ThQybpeRj9ruASx3/6OLY mWMAnjNEUD/l5/Pfi61TS6wpqcrArw5+ =5eYo -----END PGP SIGNATURE----- --2qXFWqzzG3v1+95a--