On Sat, Apr 28, 2018 at 8:56 AM, Alexander Monakov <amonakov@xxxxxxxxx> wrote:
> Not all revisions of DW I2C controller implement the enable status register.
> On platforms where that's the case (e.g. BG2CD and SPEAr ARM SoCs), waiting
> for enable will time out as reading the unimplemented register yields zero.
>
> It was observed that reading the IC_ENABLE_STATUS register once suffices to
> avoid getting it stuck on Bay Trail hardware, so replace polling with one
> dummy read of the register.
>
> Cc: Ben Gardner <gardner.ben@xxxxxxxxx>
> Cc: Jarkko Nikula <jarkko.nikula@xxxxxxxxxxxxxxx>
> Cc: Wolfram Sang <wsa@xxxxxxxxxxxxx>
> Fixes: fba4adbbf670 ("i2c: designware: must wait for enable")
> Tested-by: Ben Gardner <gardner.ben@xxxxxxxxx>
> Signed-off-by: Alexander Monakov <amonakov@xxxxxxxxx>
> ---
> drivers/i2c/busses/i2c-designware-master.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
> index fd36c39ddf4e..0cdba29ae0a9 100644
> --- a/drivers/i2c/busses/i2c-designware-master.c
> +++ b/drivers/i2c/busses/i2c-designware-master.c
> @@ -209,7 +209,10 @@ static void i2c_dw_xfer_init(struct dw_i2c_dev *dev)
> i2c_dw_disable_int(dev);
>
> /* Enable the adapter */
> - __i2c_dw_enable_and_wait(dev, true);
> + __i2c_dw_enable(dev, true);
> +
> + /* Dummy read to avoid the register getting stuck on Bay Trail */
> + dw_readl(dev, DW_IC_ENABLE_STATUS);
>
> /* Clear and enable interrupts */
> dw_readl(dev, DW_IC_CLR_INTR);
> --
Tested-by: Ben Gardner <gardner.ben@xxxxxxxxx>
Thanks.
