From mboxrd@z Thu Jan 1 00:00:00 1970 From: Song Qiang Subject: Re: [PATCH 2/2] iio: magnetometer: Add driver support for PNI RM3100 Date: Wed, 26 Sep 2018 16:09:45 +0800 Message-ID: <20180926080752.GA12183@Eros> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <4de691f2-dbc9-6124-efa6-66f2dd7e0f2b@electromag.com.au> Sender: linux-kernel-owner@vger.kernel.org To: Phil Reid 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 List-Id: devicetree@vger.kernel.org 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... 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... yours, Song Qiang