[PATCH 0/4] Cadence I2C driver fixes

Harini Katakam harinik at xilinx.com
Tue Dec 2 02:05:45 PST 2014

This series implements workarounds for some bugs in Cadence I2C controller.

- The I2C controller when configured in Master Mode generates invalid read transactions.
When HOLD bit is set and HW timeout occurs, invalid read transactions are
generated on the bus. This will affect repeated start conditions and large
data transfer condtions where transfer_size_register has to be updated again.
The transfer size register rolls over erroneously under these conditions.
Note that this HW timeout cannot be disabled even if the interrupt is unused.
Errata link: http://www.xilinx.com/support/answers/61664.html

-The I2C controller when configured in Master Mode is the missing master completion interrupt.
During repeated start condition, the driver has to set the HOLD bit for
the set of transfer being done together and clear the HOLD bit just before
the last transfer. But the controller does not indicate completion when
a read/receive transfer is done if the HOLD bit is set. This affects
all repeated start operation where a read/receive transfer is not
the last transfer.
Errata link: http://www.xilinx.com/support/answers/61665.html

To address the above,
- >252 byte transfer are done such that transfer_size never becomes zero.
- timeout register value is increased (even though the driver doesn't use this).
- repeated start is defeatured based on a devicetree input. This input is
because repeated start is required as part of protocol for some slave devices
(not just to retain control in a multi-master scenario). The driver works
as expected with these devices and hence the defeature is optional in such
- In case user chooses not to de-feature repeated start, then a check is
performed to see if there any transfer following a read/receive transfer
in the set of messages using repeated start. An error is returned in such
cases because if we proceed, completion interrupt is never obtained and
a SW timeout will occur.

Harini Katakam (1):
  i2c: cadence: Handle > 252 byte transfers

Vishnu Motghare (3):
  i2c: cadence: Set the hardware time-out register to maximum value
  devicetree: bindings: Add defeature-repeated-start property for
    Cadence I2C
  i2c: cadence: Defeature repeated start based on devicetree property

 .../devicetree/bindings/i2c/i2c-cadence.txt        |   11 ++
 drivers/i2c/busses/i2c-cadence.c                   |  200 +++++++++++---------
 2 files changed, 125 insertions(+), 86 deletions(-)


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