From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Subject: Re: [PATCH] tty/serial/pl011: don't print error msg if dmaengine_pause is not supported Date: Mon, 18 Apr 2011 16:13:40 +0100 Message-ID: <20110418151340.GB25671@n2100.arm.linux.org.uk> References: <98422bc7c3ebb4bf6a4ab26179b3f3b7d1a5b5ca.1303125086.git.viresh.kumar@st.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from caramon.arm.linux.org.uk ([78.32.30.218]:57748 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751753Ab1DRPOH (ORCPT ); Mon, 18 Apr 2011 11:14:07 -0400 Content-Disposition: inline In-Reply-To: <98422bc7c3ebb4bf6a4ab26179b3f3b7d1a5b5ca.1303125086.git.viresh.kumar@st.com> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Viresh Kumar Cc: linux-arm-kernel@lists.infradead.org, linus.walleij@stericsson.com, armando.visconti@st.com, shiraz.hashim@st.com, amit.goel@st.com, viresh.linux@gmail.com, linux-serial@vger.kernel.org On Mon, Apr 18, 2011 at 04:52:00PM +0530, Viresh Kumar wrote: > Few dma controller doesn't support dmaengine_pause() and return -ENXIO if > dmaengine_pause() is called for them. Error messages such as "unable to pause > DMA transfer" shouldn't be printed for them. It is _required_ to pause the DMA engine at this point, as we need to read characters via PIO. Leaving the DMA engine active at this point invites it to transfer additional characters beneath us, before we've had time to properly update the DMA engine for the characters received. So, dmaengine_pause() is a requirement for PL011.