Re: [PATCH v2] iio: imu: inv_mpu6050: Use as standalone trigger - Jean-Baptiste Maneyrol

From: Jean-Baptiste Maneyrol <JManeyrol@invensense.com>
To: Linus Walleij <linus.walleij@linaro.org>,
	Jonathan Cameron <jic23@kernel.org>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>
Cc: Hartmut Knaack <knaack.h@gmx.de>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Subject: Re: [PATCH v2] iio: imu: inv_mpu6050: Use as standalone trigger
Date: Thu, 25 Mar 2021 17:08:19 +0000	[thread overview]
Message-ID: <BL0PR12MB501168E715C96BBDF34D1ACCC4629@BL0PR12MB5011.namprd12.prod.outlook.com> (raw)
In-Reply-To: <20210322132408.1003443-1-linus.walleij@linaro.org>

Hello,

looks good for me, thanks for the patch. Here is my ack.

Acked-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>

We're lucky this is working without any sensor running, it was not obvious.
On which chip have you tested that?

Thanks,
JB


From: Linus Walleij <linus.walleij@linaro.org>
Sent: Monday, March 22, 2021 14:24
To: Jonathan Cameron <jic23@kernel.org>; linux-iio@vger.kernel.org <linux-iio@vger.kernel.org>
Cc: Hartmut Knaack <knaack.h@gmx.de>; Lars-Peter Clausen <lars@metafoo.de>; Peter Meerwald-Stadler <pmeerw@pmeerw.net>; Linus Walleij <linus.walleij@linaro.org>; Jean-Baptiste Maneyrol <JManeyrol@invensense.com>
Subject: [PATCH v2] iio: imu: inv_mpu6050: Use as standalone trigger 
 
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It may happen that the MPU6050 is the only hardware
trigger available on your system such as this:

> lsiio
Device 003: hscdtd008a
Device 001: mpu6050
Device 002: gp2ap002
Device 000: ab8500-gpadc
Trigger 000: mpu6050-dev1

And when you want to use it to read periodically from
your magnetometer like this:

> iio_generic_buffer -a -c 100 -n hscdtd008a -t mpu6050-dev1

Then the following happens:

[  209.951334] Internal error: Oops: 5 [#1] SMP ARM
(...)
[  209.981969] Hardware name: ST-Ericsson Ux5x0 platform (Device Tree Support)
[  209.988925] PC is at inv_scan_query_mpu6050+0x8/0xb8
[  209.993914] LR is at inv_mpu6050_set_enable+0x40/0x194

This is because since we are not using any channels from the
same device, the indio_dev->active_scan_mask is NULL.

Just checking for that and bailing out is however not enough:
we have to enable some kind of FIFO for the readout to work.
So enable the temperature as a dummy FIFO and all works
fine.

Fixes: 09a642b78523 ("Invensense MPU6050 Device Driver.")
Cc: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v1->v2:
- Add Fixes: tag, this is the initial commit but I do not
  think backporting makes sense, this is a non-regression
  non-critical fix.
- Fix a nit found by Andy (return mask value directly).
---
 drivers/iio/imu/inv_mpu6050/inv_mpu_trigger.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_trigger.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_trigger.c
index f7b5a70be30f..de8ed1446d60 100644
--- a/drivers/iio/imu/inv_mpu6050/inv_mpu_trigger.c
+++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_trigger.c
@@ -11,6 +11,16 @@ static unsigned int inv_scan_query_mpu6050(struct iio_dev *indio_dev)
         struct inv_mpu6050_state  *st = iio_priv(indio_dev);
         unsigned int mask;
 
+       /*
+        * If the MPU6050 is just used as a trigger, then the scan mask
+        * is not allocated so we simply enable the temperature channel
+        * as a dummy and bail out.
+        */
+       if (!indio_dev->active_scan_mask) {
+               st->chip_config.temp_fifo_enable = true;
+               return INV_MPU6050_SENSOR_TEMP;
+       }
+
         st->chip_config.gyro_fifo_enable =
                 test_bit(INV_MPU6050_SCAN_GYRO_X,
                          indio_dev->active_scan_mask) ||
-- 
2.29.2
