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[97.64.17.87]) by smtp.gmail.com with ESMTPSA id d65-v6sm48334221pfm.100.2018.11.02.00.55.29 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 02 Nov 2018 00:55:32 -0700 (PDT) Subject: Re: [PATCH v4 3/3] iio: magnetometer: Add driver support for PNI RM3100 To: Jonathan Cameron Cc: knaack.h@gmx.de, lars@metafoo.de, pmeerw@pmeerw.net, robh+dt@kernel.org, mark.rutland@arm.com, preid@electromag.com.au, himanshujha199640@gmail.com, linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20181002143812.3661-1-songqiang1304521@gmail.com> <20181012073536.20339-1-songqiang1304521@gmail.com> <20181012073536.20339-4-songqiang1304521@gmail.com> <20181013111935.00a2e1af@archlinux> <20181021151427.5b3dbb9b@archlinux> From: Song Qiang Message-ID: Date: Fri, 2 Nov 2018 15:55:27 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181021151427.5b3dbb9b@archlinux> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/10/21 下午10:14, Jonathan Cameron wrote: > On Thu, 18 Oct 2018 16:24:15 +0800 > Song Qiang 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; >>>> + unsigned long scan_mask = *indio_dev->active_scan_mask; >>>> + unsigned int mask_len = indio_dev->masklength; >>>> + struct rm3100_data *data = iio_priv(indio_dev); >>>> + struct regmap *regmap = data->regmap; >>>> + int ret, i, bit; >>>> + >>>> + mutex_lock(&data->lock); >>>> + switch (scan_mask) { >>>> + case BIT(0) | BIT(1) | BIT(2): >>>> + ret = regmap_bulk_read(regmap, RM3100_REG_MX2, data->buffer, 9); >>>> + mutex_unlock(&data->lock); >>>> + if (ret < 0) >>>> + goto done; >>>> + break; >>>> + case BIT(0) | BIT(1): >>>> + ret = regmap_bulk_read(regmap, RM3100_REG_MX2, data->buffer, 6); >>>> + mutex_unlock(&data->lock); >>>> + if (ret < 0) >>>> + goto done; >>>> + break; >>>> + case BIT(1) | BIT(2): >>>> + ret = regmap_bulk_read(regmap, RM3100_REG_MY2, data->buffer, 6); >>>> + mutex_unlock(&data->lock); >>>> + if (ret < 0) >>>> + goto done; >>>> + break; >>> What about BIT(0) | BIT(2)? >>> >>> Now you can do it like you have here and on that one corner case let the iio core >>> demux code take care of it, but then you will need to provide available_scan_masks >>> so the core knows it needs to handle this case. >>> >> This confused me a little. The available_scan_masks I was using is {BIT(0) | >> BIT(1) | BIT(2), 0x0}. Apparently in this version of patch I would like it to >> handle every circumstances like BIT(0), BIT(0) | BIT(2), BIT(1) | BIT(2), etc. >> Since Phil mentioned he would like this to reduce bus usage as much as we can >> and I want it, too, I think these three circumstances can be read consecutively >> while others can be read one axis at a time. So I plan to let  BIT(0) | BIT(2) >> fall into the 'default' section, which reads axis one by one. >> >> My question is, since this handles every possible combination, do I still need >> to list every available scan masks in available_scan_masks? > Ah. I see, I'd missed that the default was picking up that case as well as the > single axes. It would be interesting to sanity check if it is quicker on > a 'typical' platform to do the all axis read for the BIT(0) | BIT(2) case > and drop the middle value (which would be done using available scan_masks) > or to just do two independent reads. > > (I would guess it is worth reading the 'dead' axis). > >> >> All other problems will be fixed in the next patch. >> >> yours, >> >> Song Qiang >> >> >> ... > Thanks, > > Jonathan I tested this two ways of getting data with the following code snippet:     u8 buffer[9];     struct timeval timebefore, timeafter;     do_gettimeofday(&timebefore);     ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, 9);     if (ret < 0)         goto unlock_return;     do_gettimeofday(&timeafter);     printk(KERN_INFO "read with dead axis time: %ld",            timeafter.tv_sec * 1000000 + timeafter.tv_usec -            timebefore.tv_sec * 1000000 - timebefore.tv_usec);     do_gettimeofday(&timebefore);     ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, 3);     if (ret < 0)         goto unlock_return;     ret = regmap_bulk_read(regmap, RM3100_REG_MZ2, buffer + 6, 3);     if (ret < 0)         goto unlock_return;     do_gettimeofday(&timeafter);     printk(KERN_INFO "read two single axis time: %ld",            timeafter.tv_sec * 1000000 + timeafter.tv_usec -            timebefore.tv_sec * 1000000 - timebefore.tv_usec); And get this result: [  161.264777] read with dead axis time: 883 [  161.270621] read two single axis time: 1359 [  161.575134] read with dead axis time: 852 [  161.580973] read two single axis time: 1356 [  161.895704] read with dead axis time: 854 [  161.903744] read two single axis time: 3540 [  162.223600] read with dead axis time: 853 [  162.229451] read two single axis time: 1363 [  162.591227] read with dead axis time: 850 [  162.597630] read two single axis time: 1555 [  162.920102] read with dead axis time: 852 [  162.926467] read two single axis time: 1534 [  163.303121] read with dead axis time: 881 [  163.308997] read two single axis time: 1390 [  163.711004] read with dead axis time: 861 It seems like you're right! Reading consecutively 9 bytes does save a lot time compared to read 3 bytes twice.