From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751501AbaHOUVF (ORCPT ); Fri, 15 Aug 2014 16:21:05 -0400 Received: from www.linutronix.de ([62.245.132.108]:58333 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751109AbaHOUVD (ORCPT ); Fri, 15 Aug 2014 16:21:03 -0400 Message-ID: <53EE6BA5.2060101@linutronix.de> Date: Fri, 15 Aug 2014 22:20:53 +0200 From: Sebastian Andrzej Siewior User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.0 MIME-Version: 1.0 To: Lennart Sorensen CC: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, tony@atomide.com, balbi@ti.com, Vinod Koul , Greg Kroah-Hartman Subject: Re: [PATCH 05/15] tty: serial: Add 8250-core based omap driver References: <1408124563-31541-1-git-send-email-bigeasy@linutronix.de> <1408124563-31541-6-git-send-email-bigeasy@linutronix.de> <20140815183731.GI17769@csclub.uwaterloo.ca> <53EE5F3F.2000707@linutronix.de> <20140815193352.GC17765@csclub.uwaterloo.ca> In-Reply-To: <20140815193352.GC17765@csclub.uwaterloo.ca> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/15/2014 09:33 PM, Lennart Sorensen wrote: >> On the other hand if you use DMA then it can handle transfers > 64bytes >> in one go and you can start transfers while the FIFO is not completely >> empty. > > You can dma more than the fifo size? Yes. The UART asserts the DMA line as long as there is room for $TRESHOLD number of bytes. So we never overflow the FIFO. That is why we can't take any DMA channel but only *the* one. >> There is patch in Greg's tty tree already where you are able to >> configure the RX trigger level. We could wire this up once we agree >> which levels we want support. The OMAP supports all levels from 1…63. > > All? or just every 4 (that's what I just read in the DRA7xx docs). All. Take a look at the RX_TRIGGER constant while comparing source vs manual :) Sebastian