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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=ham 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 42489C3A589 for ; Sun, 18 Aug 2019 19:27:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0797621872 for ; Sun, 18 Aug 2019 19:27:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566156432; bh=zBUhARBmOXI6h0lyRpeDF9P3Js+wgl8uEXqldayuRZ0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=zRri/gww6wjB4jOGzVzyDzi6p/3mK15o/c2Jh9kWjVjV2MPViwDMfO4JsHN17alPy TRej5GfpBbI5FRsjPu8ZoKanwyrpa6d5p7xVa8G7YMrqw3NEQ8FlU9ox6JseIASgG8 DPcgmhsbv4RAe7CItlWgEGqnx79ZnGxQc1Wr+pjA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726261AbfHRT1L (ORCPT ); Sun, 18 Aug 2019 15:27:11 -0400 Received: from mail.kernel.org ([198.145.29.99]:45554 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726005AbfHRT1L (ORCPT ); Sun, 18 Aug 2019 15:27:11 -0400 Received: from archlinux (cpc149474-cmbg20-2-0-cust94.5-4.cable.virginm.net [82.4.196.95]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EDD0C2184E; Sun, 18 Aug 2019 19:27:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566156429; bh=zBUhARBmOXI6h0lyRpeDF9P3Js+wgl8uEXqldayuRZ0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=xCbFrwnx0vDVs0ZG3GEUXrdMwWjj5qsHXX5c8Z3YfmEMxx2/6nvfthMFrfWPpxP5w /iCTuVaMlkVChFk5lzqVFpcYBGlO2XD3jqiGDyUClrLO5qUdsIrVSOrmg7utSILhU8 5amjwXGHcDoeLqpi6UXm6HaX2AHJaV7v/cwHUdM0= Date: Sun, 18 Aug 2019 20:27:04 +0100 From: Jonathan Cameron To: Baolin Wang Cc: Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , freeman.liu@unisoc.com, Vincent Guittot , linux-iio@vger.kernel.org, LKML Subject: Re: [PATCH] iio: adc: sc27xx: Change to polling mode to read data Message-ID: <20190818202704.69e95a4d@archlinux> In-Reply-To: References: <1870ea18729f93fb36694affaf7e9443733dd988.1564035575.git.baolin.wang@linaro.org> <20190727182709.037fc595@archlinux> <20190805145037.0a03f21e@archlinux> <20190811090251.5fbd7d75@archlinux> X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-iio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org On Mon, 12 Aug 2019 10:37:44 +0800 Baolin Wang wrote: > On Sun, 11 Aug 2019 at 16:03, Jonathan Cameron wrote: > > > > On Tue, 6 Aug 2019 15:39:45 +0800 > > Baolin Wang wrote: > > > > > Hi Jonathan, > > > > > > On Mon, 5 Aug 2019 at 21:50, Jonathan Cameron wrote: > > > > > > > > On Mon, 29 Jul 2019 10:19:48 +0800 > > > > Baolin Wang wrote: > > > > > > > > > Hi Jonathan, > > > > > > > > > > On Sun, 28 Jul 2019 at 01:27, Jonathan Cameron wrote: > > > > > > > > > > > > On Thu, 25 Jul 2019 14:33:50 +0800 > > > > > > Baolin Wang wrote: > > > > > > > > > > > > > From: Freeman Liu > > > > > > > > > > > > > > On Spreadtrum platform, the headphone will read one ADC channel multiple > > > > > > > times to identify the headphone type, and the headphone identification is > > > > > > > sensitive of the ADC reading time. And we found it will take longer time > > > > > > > to reading ADC data by using interrupt mode comparing with the polling > > > > > > > mode, thus we should change to polling mode to improve the efficiency > > > > > > > of reading data, which can identify the headphone type successfully. > > > > > > > > > > > > > > Signed-off-by: Freeman Liu > > > > > > > Signed-off-by: Baolin Wang > > > > > > > > > > > > Hi, > > > > > > > > > > > > My concerns with this sort of approach is that we may be sacrificing power > > > > > > efficiency for some usecases to support one demanding one. > > > > > > > > > > > > The maximum sleep time is 1 second (I think) which is probably too long > > > > > > to poll a register for in general. > > > > > > > > > > 1 second is the timeout time, that means something wrong when reading > > > > > the data taking 1 second, and we will poll the register status every > > > > > 500 us. > > > > > From the testing, polling mode takes less time than interrupt mode > > > > > when reading ADC data multiple times, so polling mode did not > > > > > sacrifice power > > > > > efficiency. > > > > > > > > Hmm. I'll go with a probably on that, depends on interrupt response > > > > latency etc so isn't entirely obvious. Faster response doesn't necessarily > > > > mean lower power. > > > > > > > > > > > > > > > Is there some way we can bound that time and perhaps switch between > > > > > > interrupt and polling modes depending on how long we expect to wait? > > > > > > > > > > I do not think the interrupt mode is needed any more, since the ADC > > > > > reading is so fast enough usually. Thanks. > > > > The reason for interrupts in such devices is usually precisely the opposite. > > > > > > > > You do it because things are slow enough that you can go to sleep > > > > for a long time before the interrupt occurs. > > > > > > > > So question becomes whether there are circumstances in which we are > > > > running with long timescales and would benefit from using interrupts. > > > > > > From our testing, the ADC version time is usually about 100us, it will > > > be faster to get data if we poll every 50us in this case. But if we > > > change to use interrupt mode, it will take millisecond level time to > > > get data. That will cause problems for those time sensitive scenarios, > > > like headphone detection, that's the main reason we can not use > > > interrupt mode. > > > > > > For those non-time-sensitive scenarios, yes, I agree with you, the > > > interrupt mode will get a better power efficiency. But ADC driver can > > > not know what scenarios asked by consumers, so changing to polling > > > mode seems the easiest way to solve the problem, and we've applied > > > this patch in our downstream kernel for a while, we did not see any > > > other problem. > > > > > > Thanks for your comments. > > > > OK. It's not ideal but sometimes such is life ;) > > Thanks for your understanding :) > > > > > So last question - fix or not? If a fix, can I have a fixes tag > > please. > > This is a bigger patch, I am afraid it can not be merged into stable > kernel, and original code can work at most scenarios. So I think no > need add stable tag for this patch. Thanks. > Fair enough. Needed a bit of merge effort as crossed with a generic cleanup patch it seems. Anyhow, hopefully I got it right. Pushed out as testing for the autobuilders to play with it. Thanks, Jonathan