From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934422AbbHKJzn (ORCPT ); Tue, 11 Aug 2015 05:55:43 -0400 Received: from mga14.intel.com ([192.55.52.115]:7450 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933994AbbHKJzi (ORCPT ); Tue, 11 Aug 2015 05:55:38 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.15,652,1432623600"; d="scan'208";a="623250981" Date: Tue, 11 Aug 2015 15:27:28 +0530 From: Vinod Koul To: Russell King - ARM Linux Cc: Peter Hurley , Sebastian Andrzej Siewior , 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: <20150811095728.GV11789@localhost> References: <1438977619-15488-1-git-send-email-bigeasy@linutronix.de> <1438977619-15488-2-git-send-email-bigeasy@linutronix.de> <55C54D49.3090406@hurleysoftware.com> <20150808090343.GY7576@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150808090343.GY7576@n2100.arm.linux.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 08, 2015 at 10:03:43AM +0100, Russell King - ARM Linux wrote: > 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.) The API queries the capabilities for a channel. So a channel has been allocated. BUT it would not imply the direction as that is descriptor based, so should we query the capabilities for a descriptor and use those in clients ? Also the current dma_slave_caps() has been moved to framework and reports based on driver callbacks. Now we have a hardware which supports pause for one direction only so we should model it bit differently Thoughts... ?? -- ~Vinod