On 10/25/2017 11:44 PM, Peter Rosin wrote:
On 2017-10-18 04:38, Guenter Roeck wrote:
On 10/17/2017 03:16 PM, Rob Herring wrote:
On Fri, Oct 13, 2017 at 01:35:27PM -0700, Guenter Roeck wrote:
On Fri, Oct 13, 2017 at 04:26:57PM +0200, Peter Rosin wrote:
On 2017-10-13 15:50, Guenter Roeck wrote:
On 10/13/2017 02:27 AM, Peter Rosin wrote:
With a nxp,se97 chip on an atmel sama5d31 board, the I2C adapter driver
is not always capable of avoiding the 25-35 ms timeout as specified by
the SMBUS protocol. This may cause silent corruption of the last bit of
any transfer, e.g. a one is read instead of a zero if the sensor chip
times out. This also affects the eeprom half of the nxp-se97 chip, where
this silent corruption was originally noticed. Other I2C adapters probably
suffer similar issues, e.g. bit-banging comes to mind as risky...
The SMBUS register in the nxp chip is not a standard Jedec register, but
it is not special to the nxp chips either, at least the atmel chips
have the same mechanism. Therefore, do not special case this on the
manufacturer, it is opt-in via the device property anyway.
Signed-off-by: Peter Rosin <peda@xxxxxxxxxx>
---
Documentation/devicetree/bindings/hwmon/jc42.txt | 4 ++++
drivers/hwmon/jc42.c | 20 ++++++++++++++++++++
2 files changed, 24 insertions(+)
diff --git a/Documentation/devicetree/bindings/hwmon/jc42.txt b/Documentation/devicetree/bindings/hwmon/jc42.txt
index 07a250498fbb..f569db58f64a 100644
--- a/Documentation/devicetree/bindings/hwmon/jc42.txt
+++ b/Documentation/devicetree/bindings/hwmon/jc42.txt
@@ -34,6 +34,10 @@ Required properties:
- reg: I2C address
+Optional properties:
+- smbus-timeout-disable: When set, the smbus timeout function will be disabled.
+ This is not supported on all chips.
Is this only for jc24 devices or could be any smbus device?
SMBus timeout is a standard SMBus functionality, so I would say any. It is by
default enabled on an SMBus device (actually it is not just enabled, it is
mandatory). The ability to disable it comes handy if a SMBus chip is connected
to an I2C controller which does not (or not necessarily) follow SMBus rules.
I had seen that problem myself with MAX6697, and STTS751 (and its driver) also
supports it.
So, is the approach with an optional smbus-timeout-disable property documented
in .../bindings/hwmon/jc42.txt good-to-go or should it be documented in some
common SMBus client-device file? I don't fine any such beast, so I'm unsure
how to proceed in that case.
I would suggest .../bindings/hwmon/jc42.txt. Even though the functionality is
supported by various SMBus chips, it is not supported by _every_ SMBus chip.
I also found this:
https://github.com/opennetworklinux/linux/blob/master/3.2.65-1%2Bdeb7u2/patches/driver-adt7470-knob-to-disable-smbus-timeout.patch
which suggests that we should find a common solution (even though that patch
never found its way upstream).
Rob, are you ok with "smbus-timeout-disable" as suggested above ?
Thanks,
Guenter
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
