linux-kernel - Re: [RFC PATCH 0/9] iio: Fix ABBA deadlock in inv-mpu6050

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Date:	Mon, 22 Feb 2016 00:17:51 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Daniel Baluta <daniel.baluta@...el.com>
Cc:	jic23@...nel.org, knaack.h@....de, lars@...afoo.de,
	pmeerw@...erw.net, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
	lucas.demarchi@...el.com, srinivas.pandruvada@...ux.intel.com,
	ggao@...ensense.com, adi.reus@...il.com, cmo@...exis.com,
	mwelling@...e.org
Subject: Re: [RFC PATCH 0/9] iio: Fix ABBA deadlock in inv-mpu6050

On Thu, Feb 18, 2016 at 05:53:05PM +0200, Daniel Baluta wrote:
> Sending this as an RFC because I don't know if style fixes are appropriate
> for this driver and also not sure if deadlock fix is the best solution.
> 
> I2C people should only look at patches 8/9 and 9/9.
> 
> The mpu6050 accel+gyro combo has an auxiliary I2C bus, allowing for
> an auxiliary sensor to be connected (eg. a magnetometer).
> 
> The mpu can either act as an I2C master (functionality not currently
> implemented in the driver) or it can use a bypass multiplexer which
> directly connects the auxiliary I2C bus pins to the main I2C bus pins [1]
> Currently the driver implements the bypass mode via an I2C mux.
> 
> This patchset fixes a deadlock in inv-mpu6050 IMU which happens when
> magnetometer (on auxiliary I2C bus) runs in parallel with accel or gyro.
> 
> First 7 patches do some cleanup in order to make INV MPU6050 code easier
> to read.
> 
> Patch number 8 allows passing NULL select callbacks to i2c_mux_master_xfer
> and i2c_mux_smbus_xfer.
> 
> Patch number 9 actually fixes the deadlock.

We recently had a bigger patch series fixing locking problems related to
muxes. I sadly didn't have the time to review it. Can you have a look if
it helps your case?

http://thread.gmane.org/gmane.linux.drivers.i2c/26169

Thanks,

   Wolfram


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