From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7775DCA9EB9 for ; Wed, 23 Oct 2019 20:18:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5780E21872 for ; Wed, 23 Oct 2019 20:18:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407463AbfJWUSf (ORCPT ); Wed, 23 Oct 2019 16:18:35 -0400 Received: from muru.com ([72.249.23.125]:39584 "EHLO muru.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2407427AbfJWUSe (ORCPT ); Wed, 23 Oct 2019 16:18:34 -0400 Received: from atomide.com (localhost [127.0.0.1]) by muru.com (Postfix) with ESMTPS id F0A6480CF; Wed, 23 Oct 2019 20:19:06 +0000 (UTC) Date: Wed, 23 Oct 2019 13:18:29 -0700 From: Tony Lindgren To: Peter Ujfalusi Cc: Dan Williams , Vinod Koul , Alexandre Bailon , Andy Shevchenko , Bin Liu , Daniel Mack , Felipe Balbi , Grygorii Strashko , Johan Hovold , Sekhar Nori , Sebastian Andrzej Siewior , Sergei Shtylyov , dmaengine@vger.kernel.org, linux-usb@vger.kernel.org, linux-omap@vger.kernel.org, giulio.benetti@benettiengineering.com, Sebastian Reichel , Skvortsov , Yegor Yefremov Subject: Re: [PATCH] dmaengine: cppi41: Fix cppi41_dma_prep_slave_sg() when idle Message-ID: <20191023201829.GR5610@atomide.com> References: <20191023153138.23442-1-tony@atomide.com> <245e1e8f-7933-bae1-b779-239f33d4d449@ti.com> <20191023171628.GO5610@atomide.com> <5deab8a9-5796-5367-213e-90c5961b8498@ti.com> <20191023191859.GQ5610@atomide.com> <7d578fe1-2d60-4a6e-48b0-73d66c39f783@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7d578fe1-2d60-4a6e-48b0-73d66c39f783@ti.com> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org * Peter Ujfalusi [191023 19:55]: > On 10/23/19 10:18 PM, Tony Lindgren wrote: > > We'd have to allow dma consumer driver call pm_runtime_get_sync() > > on the dma device. Something similar maybe to what we have > > for phy_pm_runtime_get_sync(). Or just get the device handle for > > dma so the consumer can call pm_runtime_get_sync() on it. > > How much a pm_runtime_get_sync(dmadev) is different when it is issued by > the client driver compared to when the dma driver issues it for it's own > device? Well the consumer device could call pm_runtime_get_sync(dmadev) when the USB cable is connected for example, and then call pm_runtime_pu(dmadev) when let's say the USB cable is disconnected. Without using pm_runtime_irq_safe() we currently don't have a clear path for doing this where the pm_runtime_get_sync(dmadev) may sleep. > But I still fail to see the difference between the events before this > patch and with the case when there is a 100ms delay between prep_sg and > issue_pending. > > Before this patch: > > prep_sg() > issue_pending() <- runtime_get() / put_autosuspend() > _not_ starting transfer > runtime_resume() <- starts the transfer > > With this patch and than 100ms delay between prep_sg and issue_pending: > > prep_sg() <- runtime_get() / put_autosuspend() > runtime_resume() <- not starting transfer > issue_pending() <- runtime_get() / put_autosuspend() > starts the transfer > > With this patch, but more than 100ms delay in between: > > prep_sg() <- runtime_get() / put_autosuspend() > runtime_resume() <- not starting transfer > > 100ms delay > runtime_suspend() > issue_pending() <- runtime_get() / put_autosuspend() > _not_ starting transfer > runtime_resume() <- starts the transfer > > pm_runtime_get_sync() in issue_pending would be the solution to avoid > delayed execution, but the usb driver should not assume that DMA is > completed as soon as issue_pending returned. Oh I see. Yes the consumer driver would need to check for the completed dma transfer in all cases. The delay issues should not currently happen in the musb_ep_program() problem case as it gets called from IRQ context. And no, adding pm_runtime_get_sync() to issue_pending is not a solution. There may be clocks and regulators that need to be powered up, and we don't want to use pm_runtime_irq_safe() because of the permanent use count on the parent. Regards, Tony