From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753381AbcD0IJS (ORCPT ); Wed, 27 Apr 2016 04:09:18 -0400 Received: from mga04.intel.com ([192.55.52.120]:62547 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752447AbcD0IJJ (ORCPT ); Wed, 27 Apr 2016 04:09:09 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,540,1455004800"; d="scan'208";a="963643465" Date: Wed, 27 Apr 2016 13:45:01 +0530 From: Vinod Koul To: Sinan Kaya Cc: dmaengine@vger.kernel.org, timur@codeaurora.org, devicetree@vger.kernel.org, cov@codeaurora.org, jcm@redhat.com, shankerd@codeaurora.org, vikrams@codeaurora.org, marc.zyngier@arm.com, mark.rutland@arm.com, eric.auger@linaro.org, agross@codeaurora.org, arnd@arndb.de, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Dan Williams , Andy Shevchenko , linux-kernel@vger.kernel.org Subject: Re: [PATCH V17 2/3] dmaengine: qcom_hidma: add debugfs hooks Message-ID: <20160427081501.GV2274@localhost> References: <1460384473-5775-1-git-send-email-okaya@codeaurora.org> <1460384473-5775-3-git-send-email-okaya@codeaurora.org> <20160426033029.GB2274@localhost> <20160426162529.GK2274@localhost> <571F9D76.2060809@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <571F9D76.2060809@codeaurora.org> 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 Tue, Apr 26, 2016 at 12:55:18PM -0400, Sinan Kaya wrote: > On 4/26/2016 12:25 PM, Vinod Koul wrote: > > On Tue, Apr 26, 2016 at 08:08:16AM -0400, okaya@codeaurora.org wrote: > >> On 2016-04-25 23:30, Vinod Koul wrote: > >>> On Mon, Apr 11, 2016 at 10:21:12AM -0400, Sinan Kaya wrote: > >>> > >>>> +static int hidma_chan_stats(struct seq_file *s, void *unused) > >>>> +{ > >>>> + struct hidma_chan *mchan = s->private; > >>>> + struct hidma_desc *mdesc; > >>>> + struct hidma_dev *dmadev = mchan->dmadev; > >>>> + > >>>> + pm_runtime_get_sync(dmadev->ddev.dev); > >>> > >>> debug shouldn't power up device, why do you want to do that > >> > >> > >> Clocks are turned off while the hw is idle. I can’t reach hw > >> registers without restoring power. > > > > Hmm, have you thought about using regmap? > > > > To be honest, I didn't know what regmap is but I just read some code > and looked at how it is used. Feel free to correct me if I got it > wrong. > > Regmap seems to be designed for *slow* speed peripherals to improve frequent > accesses by the SW. It looks like it is used by MFD, SPI and I2C drivers. > > It seems to cache the register contents and flush/invalidate them only when > needed. > > The MMIO version seems to be assuming the presence of device-tree like CLK > API which doesn't exist on ACPI systems and is not portable. > > My reaction is that it is a lot of code with no added functionality to what > HIDMA driver is trying to achieve. > > Given that the use case here is only for debug purposes; I think it is OK > to keep this runtime call here. I don't want to add any overhead into the > existing code just to support the debug use case. > > None of my register read/writes are slow. This file will only be used to > troubleshoot customer issues. $ is always faster than MMIO. This way you can give reg contents to users without waking up hw. Also we at Intel use regmap on ACPI systems without CLK API -- ~Vinod