LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Andrea Merello <andrea.merello@gmail.com>
Cc: Jonathan Cameron <jic23@kernel.org>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Rob Herring <robh+dt@kernel.org>,
	Matt Ranostay <matt.ranostay@konsulko.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-iio <linux-iio@vger.kernel.org>,
	Andrea Merello <andrea.merello@iit.it>
Subject: Re: [PATCH 4/4] iio: imu: add BNO055 serdev driver
Date: Mon, 19 Jul 2021 14:55:58 +0300	[thread overview]
Message-ID: <YPVoTp3SPzL6LQ6X@smile.fi.intel.com> (raw)
In-Reply-To: <CAN8YU5M4+ZFNzLkGhP1w7Q80yKVBxAXqK=k6qYzpTYXj=+707w@mail.gmail.com>

On Mon, Jul 19, 2021 at 10:49:54AM +0200, Andrea Merello wrote:
> Il giorno sab 17 lug 2021 alle ore 17:48 Jonathan Cameron
> <jic23@kernel.org> ha scritto:
> > On Thu, 15 Jul 2021 16:17:42 +0200
> > Andrea Merello <andrea.merello@gmail.com> wrote:

...

> > > +/*
> > > + * Register writes cmd have the following format
> > > + * +------+------+-----+-----+----- ... ----+
> > > + * | 0xAA | 0xOO | REG | LEN | payload[LEN] |
> > > + * +------+------+-----+-----+----- ... ----+
> > > + *
> > > + * Register write responses have the following format
> > > + * +------+----------+
> > > + * | 0xEE | ERROCODE |
> > > + * +------+----------+
> > > + *
> > > + * Register read have the following format
> > > + * +------+------+-----+-----+
> > > + * | 0xAA | 0xO1 | REG | LEN |
> > > + * +------+------+-----+-----+
> > > + *
> > > + * Successful register read response have the following format
> > > + * +------+-----+----- ... ----+
> > > + * | 0xBB | LEN | payload[LEN] |
> > > + * +------+-----+----- ... ----+
> > > + *
> > > + * Failed register read response have the following format
> > > + * +------+--------+
> > > + * | 0xEE | ERRCODE|  (ERRCODE always > 1)
> > > + * +------+--------+
> > > + *
> > > + * Error codes are
> > > + * 01: OK
> > > + * 02: read/write FAIL
> > > + * 04: invalid address
> > > + * 05: write on RO
> > > + * 06: wrong start byte
> > > + * 07: bus overrun
> > > + * 08: len too high
> > > + * 09: len too low
> > > + * 10: bus RX byte timeout (timeout is 30mS)
> > > + *
> > > + *
> > > + * **WORKAROUND ALERT**
> > > + *
> > > + * Serial communication seems very fragile: the BNO055 buffer seems to overflow
> > > + * very easy; BNO055 seems able to sink few bytes, then it needs a brief pause.
> > > + * On the other hand, it is also picky on timeout: if there is a pause > 30mS in
> > > + * between two bytes then the transaction fails (IMU internal RX FSM resets).
> > > + *
> > > + * BMU055 has been seen also failing to process commands in case we send them
> > > + * too close each other (or if it is somehow busy?)
> > > + *
> > > + * One idea would be to split data in chunks, and then wait 1-2mS between
> > > + * chunks (we hope not to exceed 30mS delay for any reason - which should
> > > + * be pretty a lot of time for us), and eventually retry in case the BNO055
> > > + * gets upset for any reason. This seems to work in avoiding the overflow
> > > + * errors, but indeed it seems slower than just perform a retry when an overflow
> > > + * error occur.
> > > + * In particular I saw these scenarios:
> > > + * 1) If we send 2 bytes per time, then the IMU never(?) overflows.
> > > + * 2) If we send 4 bytes per time (i.e. the full header), then the IMU could
> > > + *    overflow, but it seem to sink all 4 bytes, then it returns error.
> > > + * 3) If we send more than 4 bytes, the IMU could overflow, and I saw it sending
> > > + *    error after 4 bytes are sent; we have troubles in synchronizing again,
> > > + *    because we are still sending data, and the IMU interprets it as the 1st
> > > + *    byte of a new command.
> > > + *
> > > + * So, we workaround all this in the following way:
> > > + * In case of read we don't split the header but we rely on retries; This seems
> > > + * convenient for data read (where we TX only the hdr).
> > > + * For TX we split the transmission in 2-bytes chunks so that, we should not
> > > + * only avoid case 2 (which is still manageable), but we also hopefully avoid
> > > + * case 3, that would be by far worse.
> >
> > Nice docs and this sounds terrible!
> 
> Indeed.. If anyone has nicer ideas, or is aware about better
> workaround, I would really love to know...

This needs somebody to go thru data sheet and check for possibilities, what you
described above is not gonna fly. Okay, "in a robust way".

I can't believe there is nothing in the communication protocol that may
increase a robustness.

> > > + */

...

> > > +/* Read operation overhead:
> > > + * 4 bytes req + 2byte resp hdr
> > > + * 6 bytes = 60 bit (considering 1start + 1stop bits).
> > > + * 60/115200 = ~520uS
> > > + * In 520uS we could read back about 34 bytes that means 3 samples, this means
> > > + * that in case of scattered read in which the gap is 3 samples or less it is
> > > + * still convenient to go for a burst.
> > > + * We have to take into account also IMU response time - IMU seems to be often
> > > + * reasonably quick to respond, but sometimes it seems to be in some "critical
> > > + * section" in which it delays handling of serial protocol.
> > > + * By experiment, it seems convenient to burst up to about 5/6-samples-long gap

Missed perial and entire comment needs proper style and space occupation ratio.

> > > + */

...

> > > +     enum {
> > > +             STATUS_OK = 0,  /* command OK */
> > > +             STATUS_FAIL = 1,/* IMU communicated an error */
> > > +             STATUS_CRIT = -1/* serial communication with IMU failed */

enum may be kernel doc described.

> > > +     } cmd_status;

...

> > > +static struct serdev_device_driver bno055_sl_driver = {
> > > +     .driver = {

> > > +             .name = BNO055_SL_DRIVER_NAME,

This is (semi-)ABI and preferably should be hard coded explicitly.

> > > +             .of_match_table = bno055_sl_of_match,
> > > +     },
> > > +     .probe = bno055_sl_probe,
> > > +};

-- 
With Best Regards,
Andy Shevchenko



  reply	other threads:[~2021-07-19 11:56 UTC|newest]

Thread overview: 88+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-15 14:17 [PATCH 0/4] Add support for Bosch BNO055 IMU Andrea Merello
2021-07-15 14:17 ` [PATCH 1/4] iio: add modifiers for linear acceleration Andrea Merello
2021-07-17 14:32   ` Jonathan Cameron
2021-07-15 14:17 ` [PATCH 2/4] iio: imu: add Bosch Sensortec BNO055 core driver Andrea Merello
2021-07-15 16:49   ` Andy Shevchenko
2021-07-16  9:19     ` Andrea Merello
2021-07-16 12:39       ` Andy Shevchenko
2021-07-19  7:12         ` Andrea Merello
2021-07-19 10:33         ` Andrea Merello
2021-07-19  9:02     ` Andrea Merello
2021-07-19 11:48       ` Andy Shevchenko
2021-07-19 13:13         ` Andrea Merello
2021-07-16  7:24   ` Alexandru Ardelean
2021-07-16  9:49     ` Andrea Merello
2021-07-17 15:32   ` Jonathan Cameron
2021-07-19  8:30     ` Andrea Merello
2021-07-24 17:08       ` Jonathan Cameron
2021-07-26 14:36         ` Andrea Merello
2021-07-31 18:01           ` Jonathan Cameron
2021-08-04 10:06             ` Andrea Merello
2021-08-04 16:50               ` Jonathan Cameron
2021-08-04 19:27                 ` Andy Shevchenko
2021-07-15 14:17 ` [PATCH 3/4] dt-bindings: iio: imu: add bosch BNO055 serdev driver bindings Andrea Merello
2021-07-17 15:39   ` Jonathan Cameron
2021-07-19  8:44     ` Andrea Merello
2021-07-15 14:17 ` [PATCH 4/4] iio: imu: add BNO055 serdev driver Andrea Merello
2021-07-15 17:08   ` kernel test robot
2021-07-15 18:14   ` kernel test robot
2021-07-17 15:50   ` Jonathan Cameron
2021-07-19  8:49     ` Andrea Merello
2021-07-19 11:55       ` Andy Shevchenko [this message]
2021-07-19 12:59         ` Andrea Merello
2021-07-19 14:15           ` Andy Shevchenko
2021-07-19 15:07             ` Andrea Merello
2021-10-28 10:18 ` [v2 00/10] Add support for Bosch BNO055 IMU Andrea Merello
2021-10-28 10:18   ` [v2 01/10] utils_macro: introduce find_closest_unsorted() Andrea Merello
2021-10-28 10:25     ` Andy Shevchenko
2021-11-08 11:05       ` Andrea Merello
2021-10-28 10:18   ` [v2 02/10] iio: document linear acceleration modifiers Andrea Merello
2021-10-28 10:31     ` Andy Shevchenko
2021-11-09  7:48       ` Andrea Merello
2021-10-28 10:40     ` Jonathan Cameron
2021-11-09  8:00       ` Andrea Merello
2021-11-09 17:00         ` Jonathan Cameron
2021-10-28 10:18   ` [v2 03/10] iio: document euler angles modifiers Andrea Merello
2021-10-28 10:33     ` Andy Shevchenko
2021-10-28 10:41     ` Jonathan Cameron
2021-11-09  8:15       ` Andrea Merello
2021-11-09 17:03         ` Jonathan Cameron
2021-10-28 10:18   ` [v2 04/10] iio: add modifiers for linear acceleration Andrea Merello
2021-10-28 10:45     ` Jonathan Cameron
2021-11-09  9:58       ` Andrea Merello
2021-11-09 17:05         ` Jonathan Cameron
2021-10-28 10:18   ` [v2 05/10] iio: add modifers for pitch, yaw, roll Andrea Merello
2021-10-28 10:47     ` Jonathan Cameron
2021-10-28 10:18   ` [v2 06/10] iio: document bno055 private sysfs attributes Andrea Merello
2021-10-28 11:04     ` Jonathan Cameron
2021-11-09 10:22       ` Andrea Merello
2021-11-14 16:20         ` Jonathan Cameron
2022-01-04 11:42           ` Andrea Merello
2022-01-15 15:27             ` Jonathan Cameron
2022-01-17  9:37               ` Andrea Merello
2021-10-28 10:18   ` [v2 07/10] iio: imu: add Bosch Sensortec BNO055 core driver Andrea Merello
2021-10-28 13:31     ` Jonathan Cameron
2021-11-09 11:52       ` Andrea Merello
2021-11-14 16:33         ` Jonathan Cameron
2021-10-28 10:18   ` [v2 08/10] dt-bindings: iio: imu: add documentation for Bosch BNO055 bindings Andrea Merello
2021-10-28 12:25     ` Rob Herring
2021-10-28 10:18   ` [v2 09/10] iio: imu: add BNO055 serdev driver Andrea Merello
2021-10-28 12:31     ` Jonathan Cameron
2021-11-09 15:33       ` Andrea Merello
2021-11-14 16:37         ` Jonathan Cameron
2021-10-29  7:09     ` kernel test robot
2021-10-29 12:59     ` kernel test robot
2021-10-28 10:18   ` [v2 10/10] iio: imu: add BNO055 I2C driver Andrea Merello
2021-10-28 11:10     ` Jonathan Cameron
2021-11-11 10:12       ` Andrea Merello
2021-11-14 16:38         ` Jonathan Cameron
2021-10-28 22:04     ` Randy Dunlap
2021-11-09 11:56       ` Andrea Merello
2021-11-09 15:47         ` Randy Dunlap
2021-11-09 18:21           ` Joe Perches
2021-11-09 19:11             ` Randy Dunlap
2021-11-09 20:46               ` Joe Perches
2021-11-09 21:20                 ` Randy Dunlap
2021-10-29 13:30     ` kernel test robot
2021-10-28 10:35   ` [v2 00/10] Add support for Bosch BNO055 IMU Jonathan Cameron
2021-10-28 10:33     ` Andy Shevchenko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YPVoTp3SPzL6LQ6X@smile.fi.intel.com \
    --to=andriy.shevchenko@linux.intel.com \
    --cc=andrea.merello@gmail.com \
    --cc=andrea.merello@iit.it \
    --cc=jic23@kernel.org \
    --cc=lars@metafoo.de \
    --cc=linux-iio@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=matt.ranostay@konsulko.com \
    --cc=robh+dt@kernel.org \
    --subject='Re: [PATCH 4/4] iio: imu: add BNO055 serdev driver' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).