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List:       linux-i2c
Subject:    Re: [PATCH v2 1/2] i2c: designware: fix poll-after-enable regression
From:       Ben Gardner <gardner.ben () gmail ! com>
Date:       2018-04-30 16:08:33
Message-ID: CAE7DoPYdLYd9mKRbMOT5hALnfEeWboqBJutCLDeV8T=L6Qat=g () mail ! gmail ! com
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On Sat, Apr 28, 2018 at 8:56 AM, Alexander Monakov <amonakov@ispras.ru> 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@gmail.com>
> Cc: Jarkko Nikula <jarkko.nikula@linux.intel.com>
> Cc: Wolfram Sang <wsa@the-dreams.de>
> Fixes: fba4adbbf670 ("i2c: designware: must wait for enable")
> Tested-by: Ben Gardner <gardner.ben@gmail.com>
> Signed-off-by: Alexander Monakov <amonakov@ispras.ru>
> ---
>  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@gmail.com>

Thanks.
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