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From: Song Qiang <songqiang1304521@gmail.com>
To: Jonathan Cameron <jic23@kernel.org>
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
Subject: Re: [PATCH v4 3/3] iio: magnetometer: Add driver support for PNI RM3100
Date: Fri, 2 Nov 2018 15:55:27 +0800	[thread overview]
Message-ID: <b7078a05-c40b-eba5-73f6-d5e3940d88f2@gmail.com> (raw)
In-Reply-To: <20181021151427.5b3dbb9b@archlinux>


On 2018/10/21 下午10:14, Jonathan Cameron wrote:
> On Thu, 18 Oct 2018 16:24:15 +0800
> Song Qiang <songqiang1304521@gmail.com> 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.


  reply	other threads:[~2018-11-02  7:55 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
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 [this message]
2018-11-02  9:24               ` Jonathan Cameron
2018-11-05  0:39                 ` Song Qiang

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