[PATCH v2 0/2] Sluggish AT91 I2C driver causes SMBus timeouts

Peter Rosin
2017-11-27T16:31:16Z

Hi!

[I was waiting for a comment from Rob for the initial submission,
but that never came and I nearly forgot. Instead of pinging again,
I'm resubmitting with the review comment from Guenter fixed, hoping
that Rob will react this time.]

This is a workaround for a problem in the AT91 I2C adapter driver
(or perhaps the hardware?) when it drives the TWI peripheral on an
Atmel sama5d3 chip as I2C.

Apparently, that driver can delay in excess of 100 ms just after
the transfer of the 7th bit of the last byte. When it does this
the I2C bus, when viewed from SMBUS client devices, appears
stuck with SCL low. Some SMBUS devices times out under these
conditions, in particular temperature sensors. The I2C adapter
driver does however not notice the timeout, and thinks the transfer
completed successfully when it finally desides to finish the
transaction. When this happens, the 8th bit of the last byte is
always set, and thus quite possibly corrupted.

The chip this was observed with (an nxp SE97) has a means to disable
the SMBUS timeout detector, which "fixes" things. Do that.

This should probably go to stable?

Previous discussion: https://lkml.org/lkml/2017/10/12/227

Changes since v1: https://lkml.org/lkml/2017/10/13/184
- Added #include of bitops.h
- Rebased to v4.15-rc1

Cheers,
Peter

Peter Rosin (2):
hwmon: (jc42) optionally try to disable the SMBUS timeout
ARM: dts: at91: disable the nxp,se97b SMBUS timeout on the TSE-850

Documentation/devicetree/bindings/hwmon/jc42.txt | 4 ++++
arch/arm/boot/dts/at91-tse850-3.dts | 1 +
drivers/hwmon/jc42.c | 21 +++++++++++++++++++++
3 files changed, 26 insertions(+)

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2.11.0