From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755043AbaKEOFh (ORCPT ); Wed, 5 Nov 2014 09:05:37 -0500 Received: from mga02.intel.com ([134.134.136.20]:62365 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753996AbaKEOFe (ORCPT ); Wed, 5 Nov 2014 09:05:34 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.07,320,1413270000"; d="scan'208";a="602747162" Date: Wed, 5 Nov 2014 19:34:01 +0530 From: Vinod Koul To: Russell King - ARM Linux Cc: Laurent Pinchart , Krzysztof Kozlowski , Pavel Machek , "Rafael J. Wysocki" , Len Brown , Jonathan Corbet , Dan Williams , Ulf Hansson , Alan Stern , linux-pm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, Lars-Peter Clausen , Michal Simek , Kyungmin Park , Marek Szyprowski , Bartlomiej Zolnierkiewicz Subject: Re: [PATCH v8 1/5] PM / Runtime: Add getter for querying the IRQ safe option Message-ID: <20141105140401.GO1870@intel.com> References: <1413795888-18559-1-git-send-email-k.kozlowski@samsung.com> <20141031142241.GA17547@amd> <1414766416.6537.6.camel@AMDC1943> <3452823.YQ5FR2FtKz@avalon> <20141103162728.GB1870@intel.com> <20141103170408.GD4042@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141103170408.GD4042@n2100.arm.linux.org.uk> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 03, 2014 at 05:04:08PM +0000, Russell King - ARM Linux wrote: > On Mon, Nov 03, 2014 at 09:57:28PM +0530, Vinod Koul wrote: > > On Sat, Nov 01, 2014 at 02:29:42AM +0200, Laurent Pinchart wrote: > > > Many other drivers suffer from the same problem. While I won't reject your > > > proposed fix, I would prefer a more generic approach. > > > > > > One option that has been discussed previously was to use a work queue to delay > > > starting the DMA transfer to an interruptible context where > > > pm_runtime_get_sync() could be called. However, as Russell pointed out [1], > > > even that won't work in all cases as the DMA slave might need the transfer to > > > be started before enabling part of its hardware (OMAP audio seem to be such a > > > case). > > > > > > I've heard a rumor of a possible DMA engine rework to forbid calling the > > > descriptor preparation API from atomic context. This could be used as a base > > > to implement runtime PM, as DMA slave drivers should not prepare descriptors > > > if they don't need to use them. However that's a long term plan, and we need a > > > solution sooner than that. > > > > Well it is not a rumour :) > > > > I have been contemplating that now that async_tx will be killed so we dont > > have to worry about that usage. For the slave dma usage, we can change the > > prepare API to be non atomic. I think the users will be okay with approach. > > This way drivers can use runtime pm calls in prepare. > > Except we /do/ have a fair number of places where the prep calls are made > from atomic contexts, particularly in serial drivers. You'd need to > introduce a tasklet into almost every serial driver which doesn't > already have one to restart RX DMA after an error or pause. Eg, > > drivers/tty/serial/amba-pl011.c > drivers/tty/serial/pch_uart.c > drivers/tty/serial/imx.c > > Probably also: > > drivers/net/ethernet/micrel/ks8842.c > > There could well be other places as well, I've not gone through and > checked exhaustively. Yes that would be required to be done first. Or is there any better alternative proposal, am all ears -- ~Vinod