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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 23787C43382 for ; Thu, 27 Sep 2018 01:57:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA6072156D for ; Thu, 27 Sep 2018 01:57:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DA6072156D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=electromag.com.au Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727264AbeI0INV (ORCPT ); Thu, 27 Sep 2018 04:13:21 -0400 Received: from anchovy1.45ru.net.au ([203.30.46.145]:52832 "EHLO anchovy1.45ru.net.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727158AbeI0INV (ORCPT ); Thu, 27 Sep 2018 04:13:21 -0400 Received: (qmail 7351 invoked by uid 5089); 27 Sep 2018 01:57:28 -0000 Received: by simscan 1.2.0 ppid: 7274, pid: 7275, t: 0.5176s scanners: regex: 1.2.0 attach: 1.2.0 clamav: 0.88.3/m:40/d:1950 spam: 3.1.4 X-RBL: $rbltext Received: from unknown (HELO ?192.168.0.122?) (preid@electromag.com.au@203.59.235.95) by anchovy1.45ru.net.au with ESMTPA; 27 Sep 2018 01:57:27 -0000 Subject: Re: [PATCH 2/2] iio: magnetometer: Add driver support for PNI RM3100 To: Song Qiang Cc: Jonathan Cameron , jic23@kernel.org, knaack.h@gmx.de, lars@metafoo.de, pmeerw@pmeerw.net, robh+dt@kernel.org, mark.rutland@arm.com, rtresidd@electromag.com.au, linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20180925031724.21399-1-songqiang1304521@gmail.com> <20180925031724.21399-2-songqiang1304521@gmail.com> <20180925143054.00007fcb@huawei.com> <57d8a9d6-c402-068e-0a21-bbd6c20a7816@electromag.com.au> <20180926014951.GA7094@Eros> <4de691f2-dbc9-6124-efa6-66f2dd7e0f2b@electromag.com.au> <20180926080752.GA12183@Eros> From: Phil Reid Message-ID: Date: Thu, 27 Sep 2018 09:57:24 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180926080752.GA12183@Eros> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-AU Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26/09/2018 4:09 PM, Song Qiang wrote: > On Wed, Sep 26, 2018 at 10:30:34AM +0800, Phil Reid wrote: >> On 26/09/2018 9:49 AM, Song Qiang wrote: >>> On Tue, Sep 25, 2018 at 10:36:54PM +0800, Phil Reid wrote: >>>> On 25/09/2018 9:30 PM, Jonathan Cameron wrote: >>>>>> +static irqreturn_t rm3100_trigger_handler(int irq, void *p) >>>>>> +{ >>>>>> + struct iio_poll_func *pf = p; >>>>>> + struct iio_dev *indio_dev = pf->indio_dev; >>>>>> + struct rm3100_data *data = iio_priv(indio_dev); >>>>>> + struct regmap *regmap = data->regmap; >>>>>> + u8 buffer[9]; >>>>>> + int ret; >>>>>> + int i; >>>>>> + >>>>>> + mutex_lock(&data->lock); >>>>>> + ret = rm3100_wait_measurement(data); >>>>>> + if (ret < 0) { >>>>>> + mutex_unlock(&data->lock); >>>>>> + goto done; >>>>>> + } >>>>>> + >>>>>> + ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, sizeof(buffer)); >>>>>> + mutex_unlock(&data->lock); >>>>>> + if (ret < 0) >>>>>> + goto done; >>>>>> + >>>>>> + /* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */ >>>>>> + for (i = 0; i < 3; i++) >>>>>> + memcpy(data->buffer + i * 4, buffer + i * 3, 3); >>>>> Firstly X doesn't need copying. >>>>> Secondly the copy of Y actually overwrites the value of Z >>>>> XXXYYYZZZxxx >>>>> XXXxYYYZZxxx >>>>> XXXxYYYxYZZx >>>>> >>>>> I think... >>>>> >>>>>> + >>>>>> + iio_push_to_buffers_with_timestamp(indio_dev, data->buffer, >>>>>> + iio_get_time_ns(indio_dev)); >>>> >>>> memcpy target is a different buffer so should be ok. >>>> >>>> But that raises the question of does it need to be? >>>> 'buffer' could be 12 bytes long and just shuffle Z then Y. >>>> Do the unused bytes need to be zeroed? or does libiio mask them anyway? >>>> >>>> >>>> >>>> -- >>>> Regards >>>> Phil Reid >>> >>> Hi Phil, >>> >>> This is interesting, last patch I submitted uses three transactions and >>> shuffles X, Y and Z respectively. You said it should be better to use one >>> transactions, I thought it makes point, and one transaction may reduce >>> IO pressure of the i2c bus. :) >>> And that's not necessary for unused bytes to be zero. I'm not familiar >>> with libiio, actually just been studying it, can't say anything about >>> it. >>> >>> yours, >>> Song Qiang >>> >>> >> G'day Song, >> >> yes the one transaction suggestion was to reduce pressure on the bus. >> I think also with 3 calls you can up up with other devices taking over >> the i2c / spi bus in between. >> >> We've got a devkit for this part, but haven't got to wiring it up to our system as yet. >> We're looking at using the i2c interface which could push things at max samplerate, so yes I'm >> keen to see bus pressure reduced as much as possible. >> >> I was thinking something like the following: >> >> u8 buffer[12]; >> regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, 9); >> >> buffer[10] = buffer[8]; // or memcpy or some other fancy shuffle code. >> buffer[9] = buffer[7]; >> buffer[8] = buffer[6]; >> >> buffer[6] = buffer[5]; >> buffer[5] = buffer[4]; >> buffer[4] = buffer[3]; >> >> iio_push_to_buffers_with_timestamp(indio_dev, buffer, iio_get_time_ns(indio_dev)); >> >> but I'm unsure if this would be needed: >> buffer[7] = 0 >> buffer[3] = 0 >> >> What you've got does the job I think. >> >> I haven't dug into the datasheet in great detail, and my iio knownledge is limited. >> Are you sure the RM3100_CHANNEL scantype endianness is IIO_LE. >> rm3100_read_mag looks to be doing big endian conversion and the datasheet agrees with that. >> >> >> -- >> Regards >> Phil Reid >> > > Hi Phil, > > You're absolutely right! > This should be big endian, I think I probably just want something there > when I was writing this code, planned to change it later, but apparently > I've forgotten it... > > AFAIK, filling places we do not need with 0 is not needed, we just > extract valid data from valid bit field(24 here). > > Both one transaction and three transactions way have their point, but > this is a OS, probably the spiltted one is better, I need some real > thinking about this... The one transaction is better. Reduces i2c traffic by 6 bytes and ensure the measurements are tightly coupled in time for the 3 axis. > > I could have use the same buffer to read from the sensor and send it to > userspace like this: > > int i = 0; > ret = regmap_bulk_read(regmap, RM3100_REG_MX2, 9); > if(ret) > ... > /* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. */ > for (i = 0; i < 2; i++) > memcpy(buffer + (2 - i) * 4, buffer + (2 - i) * 3), 3); > > This code snippet will use the same buffer, actually that's what I was > using the first time. Jonathan must thinks so, from what he commented, > he assumed I was using the same buffer, also what you want. > But I changed this due to Peter's comment, maybe not a big deal, he > suggests to use sizeof(buffer), this makes me use an additional size 9 > buffer. I thought this doesn't matter too much, just some additional > space from the stack, but now I think maybe less memory using would be > better... > After all, this length 9 seems like never shouldn't be changed... yes that does the job. -- Regards Phil Reid