From: Phil Reid <preid@electromag.com.au>
To: Song Qiang <songqiang1304521@gmail.com>
Cc: Jonathan Cameron <jonathan.cameron@huawei.com>,
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
Subject: Re: [PATCH 2/2] iio: magnetometer: Add driver support for PNI RM3100
Date: Thu, 27 Sep 2018 09:57:24 +0800 [thread overview]
Message-ID: <ef710cc6-4a2a-ce9d-3e4c-502aea7fcf27@electromag.com.au> (raw)
In-Reply-To: <20180926080752.GA12183@Eros>
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
next prev parent reply other threads:[~2018-09-27 1:57 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-25 3:17 [PATCH 1/2] iio: magnetometer: Add DT support for PNI RM3100 Song Qiang
2018-09-25 3:17 ` [PATCH 2/2] iio: magnetometer: Add driver " Song Qiang
2018-09-25 13:30 ` Jonathan Cameron
2018-09-25 14:36 ` Phil Reid
2018-09-26 1:49 ` Song Qiang
2018-09-26 2:30 ` Phil Reid
2018-09-26 8:09 ` Song Qiang
2018-09-27 1:57 ` Phil Reid [this message]
2018-09-29 11:37 ` Jonathan Cameron
2018-09-26 1:33 ` Song Qiang
2018-09-29 11:45 ` Jonathan Cameron
2018-09-25 17:50 ` Himanshu Jha
2018-09-26 2:24 ` Song Qiang
2018-09-25 13:05 ` [PATCH 1/2] iio: magnetometer: Add DT " Jonathan Cameron
2018-10-02 14:38 ` [PATCH v3 0/3] Add support for PNI RM3100 magnetometer Song Qiang
2018-10-02 14:38 ` [PATCH v3 1/3] dt-bindings: Add PNI to the vendor prefixes Song Qiang
2018-10-02 14:38 ` [PATCH v3 2/3] dt-bindings: Add PNI RM3100 device tree binding Song Qiang
2018-10-07 15:18 ` Jonathan Cameron
2018-10-07 15:20 ` Jonathan Cameron
2018-10-02 14:38 ` [PATCH v3 3/3] iio: magnetometer: Add driver support for PNI RM3100 Song Qiang
2018-10-03 1:42 ` Phil Reid
2018-10-07 15:07 ` Jonathan Cameron
2018-10-07 15:44 ` Jonathan Cameron
2018-10-11 4:35 ` Song Qiang
2018-10-13 9:24 ` Jonathan Cameron
2018-10-12 7:35 ` [PATCH v4 0/3] Add support for PNI RM3100 magnetometer Song Qiang
2018-10-12 7:35 ` [PATCH v4 1/3] dt-bindings: Add PNI to the vendor prefixes Song Qiang
2018-10-12 11:36 ` Rob Herring
2018-10-12 7:35 ` [PATCH v4 2/3] iio: magnetometer: Add DT support for PNI RM3100 Song Qiang
2018-10-12 11:37 ` Rob Herring
2018-10-12 7:35 ` [PATCH v4 3/3] iio: magnetometer: Add driver " Song Qiang
2018-10-12 8:36 ` Song Qiang
2018-10-12 12:53 ` Himanshu Jha
2018-10-17 8:00 ` Song Qiang
2018-10-21 14:08 ` Jonathan Cameron
2018-10-13 10:19 ` Jonathan Cameron
2018-10-18 8:24 ` Song Qiang
2018-10-21 14:14 ` Jonathan Cameron
2018-11-02 7:55 ` Song Qiang
2018-11-02 9:24 ` Jonathan Cameron
2018-11-05 0:39 ` Song Qiang
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