On Sun, 23 Jul 2017, Furquan Shaikh wrote:
> Commit 274e43edcda6f ("mfd: intel-lpss: Do not put device in reset
> state on suspend") changed the behavior on suspend by not putting LPSS
> controllers into reset. This was done because S3/S0ix fail if UART
> device is put into reset and no_console_suspend flag is enabled.
>
> Because of the above change, I2C controller gets into a bad state if
> it observes that the I2C lines are pulled low when power to I2C device
> is cut off during suspend (generally, I2C lines are pulled to power
> rail of the I2C device in order to ensure that there is no leakage
> because of the pulls when device is turned off). This results in the
> controller timing out for all future I2C operations after resume. It
> is primarily because of the following sequence of operations:
>
> During suspend:
> 1. I2C controller is disabled, but it is not put into reset.
> 2. Power to I2C device is cut off.
> 3. #2 results in the I2C lines being pulled low.
>
> ==> At this point the I2C controller gets into a bad state
>
> On resume:
> 1. Power to I2C device is enabled.
> 2. #2 results in the I2C lines being pulled high.
> 3. I2C controller is enabled.
>
> However, even after enabling the I2C controller, all future I2C xfers
> fail since the controller is in a bad state and does not attempt to
> make any transactions and hence times out.
>
> In order to ensure that the controller does not get into a bad state,
> this change puts it into reset if the controller type is not
> UART. With this change, the order of operations is:
>
> During suspend:
> 1. I2C controller is disabled and put into reset.
> 2. Power to I2C device is cut off.
> 3. #2 results in the I2C lines being pulled low.
>
> On resume:
> 1. Power to I2C device is enabled.
> 2. #2 results in the I2C lines being pulled high.
> 3. I2C controller is enabled and taken out of reset.
>
> Signed-off-by: Furquan Shaikh <furq...@google.com>
> ---
> drivers/mfd/intel-lpss.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
Applied, thanks.
--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
