From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752037AbaKCJgo (ORCPT ); Mon, 3 Nov 2014 04:36:44 -0500 Received: from mailout2.w1.samsung.com ([210.118.77.12]:11753 "EHLO mailout2.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751247AbaKCJgk (ORCPT ); Mon, 3 Nov 2014 04:36:40 -0500 MIME-version: 1.0 Content-type: text/plain; charset=UTF-8 X-AuditID: cbfec7f4-b7f6c6d00000120b-41-54574ca5c6a1 Content-transfer-encoding: 8BIT Message-id: <1415007395.4241.18.camel@AMDC1943> Subject: Re: [PATCH v8 1/5] PM / Runtime: Add getter for querying the IRQ safe option From: Krzysztof Kozlowski To: Laurent Pinchart Cc: Pavel Machek , "Rafael J. Wysocki" , Len Brown , Jonathan Corbet , Russell King , Dan Williams , Vinod Koul , 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 Date: Mon, 03 Nov 2014 10:36:35 +0100 In-reply-to: <3452823.YQ5FR2FtKz@avalon> References: <1413795888-18559-1-git-send-email-k.kozlowski@samsung.com> <20141031142241.GA17547@amd> <1414766416.6537.6.camel@AMDC1943> <3452823.YQ5FR2FtKz@avalon> X-Mailer: Evolution 3.10.4-0ubuntu2 X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFprBIsWRmVeSWpSXmKPExsVy+t/xa7pLfcJDDJa+YbPYOGM9q8WTA+2M FtOnXmC0WD31L6vF2aY37BZLJs9nteicuITdYtaUvUwWC9uWsFhc3jWHzeJz7xFGi9uXeS3W HrnLbvHuZYTF3VNH2SzOnL7EajHh9wU2i+Nrwy1e9u1ncRD2aGnuYfOY3TGT1WPxnpdMHneu 7WHzWNw3mdVjyZtDrB5brrazeMy++4PRo2/LKkaPFau/s3t83iTnsffzb5YAnigum5TUnMyy 1CJ9uwSujO8fr7MVTJeqeHP+FGMD43mRLkZODgkBE4mtWxtYIWwxiQv31rN1MXJxCAksZZR4 MekaO0iCV0BQ4sfkeyxdjBwczALyEkcuZYOEmQXUJSbNW8QMUf+ZUeL8xsNsEPX6EpcudzCB 2MIC4RL3l20BW8AmYCyxefkSsBoRAQuJ3kXTGUGamQVWsUp8XLuYCWQBi4CqxPZn0iA1nAIa Er8n9kEdtJxRoulnByNIjYSAskRjv9sERoFZSM6bhXDeLCTnLWBkXsUomlqaXFCclJ5rqFec mFtcmpeul5yfu4kREptfdjAuPmZ1iFGAg1GJh3fC5bAQIdbEsuLK3EOMEhzMSiK8PTrhIUK8 KYmVValF+fFFpTmpxYcYmTg4pRoYi5vMbQNYuBv6GIKOqxhPfnNDgjVgysp8Na61K6UXVgox 7/nO7jBnMjNj+792pv4Hm12PyHZvvv3vyDW51ZpT08Nt/NVVZV+um2dx8tNjN99/2vI/1HWX 9W7U7HFq15p1Pf7X+7/rfie9PBx+LDSG+abytTunLH4qbi/4FV2k5rmpK3tFTsorJZbijERD Leai4kQA7cO6C6sCAAA= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On sob, 2014-11-01 at 02:29 +0200, Laurent Pinchart wrote: > Hi Krzysztof, > > On Friday 31 October 2014 15:40:16 Krzysztof Kozlowski wrote: > > On pią, 2014-10-31 at 15:22 +0100, Pavel Machek wrote: > > > On Fri 2014-10-31 10:14:55, Krzysztof Kozlowski wrote: > > >> On pon, 2014-10-20 at 11:04 +0200, Krzysztof Kozlowski wrote: > > >>> Add a simple getter pm_runtime_is_irq_safe() for querying whether > > >>> runtime PM IRQ safe was set or not. > > >>> > > >>> Various bus drivers implementing runtime PM may use choose to suspend > > >>> differently based on IRQ safeness status of child driver (e.g. do not > > >>> unprepare the clock if IRQ safe is not set). > > >>> > > >>> Signed-off-by: Krzysztof Kozlowski > > >>> Reviewed-by: Ulf Hansson > > >> > > >> Rafael, Len, Pavel, > > >> > > >> Is proposed API ok? Do you have any comments? > > >> > > >> I'll upload whole patchset to Russell's patch tracking system. However > > >> an ack from PM maintainer is probably needed. > > > > > > I don't like the API. Having callbacks work in different context (irq > > > / noirq) based on what another function reports is ugly. > > > > > > What is the penalty if we always decide callbacks are not IRQ safe? > > > > Then pm_runtime_get_sync() could not be called in atomic context. The > > pl330 runtime PM would have to be completely reworked because one > > pm_runtime_get_sync() is called in device_issue_pending which cannot > > sleep (at least in non preemptible kernels). Probably this can be solved > > some way... > > 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. > > I've been toying with the idea of adding explicit open/close (or whatever we > would call them) operations to the DMA engine API. Those would be used by DMA > slave drivers to signal that they will start/stop using the DMA engine. > > If (1) we must start the DMA synchronously with a DMA slave call, (2) need to > sleep to handle PM, and (3) don't want to keep the DMA engine powered for as > long as one channel is requested, then we need to turn at least preparation as > not callable in atomic context, or introduce a new operation. > > [1] http://www.spinics.net/lists/dmaengine/msg01548.html That makes sense. However I am not familiar with DMA core code as much as I think it would be needed to make such generic changes :). I'll stick to one driver for now. Thanks for comments! Krzysztof