From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754404AbbHHJED (ORCPT ); Sat, 8 Aug 2015 05:04:03 -0400 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:44311 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754206AbbHHJD7 (ORCPT ); Sat, 8 Aug 2015 05:03:59 -0400 Date: Sat, 8 Aug 2015 10:03:43 +0100 From: Russell King - ARM Linux To: Peter Hurley Cc: Sebastian Andrzej Siewior , Vinod Koul , Dan Williams , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, nsekhar@ti.com, linux-omap@vger.kernel.org, linux-serial@vger.kernel.org, john.ogness@linutronix.de, Peter Ujfalusi Subject: Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause is not supported Message-ID: <20150808090343.GY7576@n2100.arm.linux.org.uk> References: <1438977619-15488-1-git-send-email-bigeasy@linutronix.de> <1438977619-15488-2-git-send-email-bigeasy@linutronix.de> <55C54D49.3090406@hurleysoftware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55C54D49.3090406@hurleysoftware.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 07, 2015 at 08:28:57PM -0400, Peter Hurley wrote: > Even dma_get_slave_caps() returns _true_ for cmd_pause support; ok, that > interface is pointless. How about reporting that as a bug then, because if you look back in the git history, as you are fully capable of, you will find that the slave capability stuff went in _after_ omap-dma, and *many* DMA engine drivers have not been updated. Here, let me do _your_ work for you: commit cb8cea513c80db1dfe2dce468d2d0772005bb9a1 Author: Maxime Ripard Date: Mon Nov 17 14:42:04 2014 +0100 dmaengine: Create a generic dma_slave_caps callback commit 2dcdf570936168d488acf90be9b04a3d32dafce7 Author: Peter Ujfalusi Date: Fri Sep 14 15:05:45 2012 +0300 dmaengine: omap: Add support for pause/resume in cyclic dma mode Oh look, omap-dma pre-dates the creation of dma_slave_caps by over two years! However, it's *not* as trivial as you think: the dma_slave_caps() call has no knowledge whether a channel will be used in cyclic mode or not, or which direction it will be used. So, it really _can't_ report whether pause mode is supported or not. So actually, this is something that can't be fixed trivially, and was a detail missed when the slave caps was reviewed (I probably missed the review or missed the point.) So, how about you stop playing the blame game and trying to shovel your shit onto DMA engine. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net.