On 29.09.2016 16:04, Jarkko Nikula wrote:
> By the specification SDA RX hold time extends incoming SDA low to high
> transition by n * ic_clk cycles but only when SCL is high. However it
> seems to help avoid above faulty arbitration lost error.
>
> Bits 23:16 in IC_SDA_HOLD register define the SDA RX hold time for the
> receiver. Be conservative and enable 1 ic_clk cycle long hold time in
> case boot firmware hasn't set it up.
>
> Reported-by: Jukka Laitinen <jukka.laitinen@xxxxxxxxx>
> Signed-off-by: Jarkko Nikula <jarkko.nikula@xxxxxxxxxxxxxxx>
> ---
> drivers/i2c/busses/i2c-designware-core.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> index 1fe93c43215c..11e866d05368 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -95,6 +95,9 @@
> #define DW_IC_STATUS_TFE BIT(2)
> #define DW_IC_STATUS_MST_ACTIVITY BIT(5)
>
> +#define DW_IC_SDA_HOLD_RX_SHIFT 16
> +#define DW_IC_SDA_HOLD_RX_MASK GENMASK(23, DW_IC_SDA_HOLD_RX_SHIFT)
> +
> #define DW_IC_ERR_TX_ABRT 0x1
>
> #define DW_IC_TAR_10BITADDR_MASTER BIT(12)
> @@ -420,12 +423,20 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
> /* Configure SDA Hold Time if required */
> reg = dw_readl(dev, DW_IC_COMP_VERSION);
> if (reg >= DW_IC_SDA_HOLD_MIN_VERS) {
> - if (dev->sda_hold_time) {
> - dw_writel(dev, dev->sda_hold_time, DW_IC_SDA_HOLD);
> - } else {
> + if (!dev->sda_hold_time) {
> /* Keep previous hold time setting if no one set it */
> dev->sda_hold_time = dw_readl(dev, DW_IC_SDA_HOLD);
> }
> + /*
> + * Workaround for avoiding TX arbitration lost in case I2C
> + * slave pulls SDA down "too quickly" after falling egde of
> + * SCL by enabling non-zero SDA RX hold. Specification says it
> + * extends incoming SDA low to high transition while SCL is
> + * high but it apprears to help also above issue.
> + */
> + if (!(dev->sda_hold_time & DW_IC_SDA_HOLD_RX_MASK))
> + dev->sda_hold_time |= 1 << DW_IC_SDA_HOLD_RX_SHIFT;
> + dw_writel(dev, dev->sda_hold_time, DW_IC_SDA_HOLD);
> } else {
> dev_warn(dev->dev,
> "Hardware too old to adjust SDA hold time.\n");
>
Tested-by: Jukka Laitinen <jukka.laitinen@xxxxxxxxx>
Tested with kabylake cpu and Ubuntu 16.04 + kernel 4.8-rc6 + ubuntu
sauce from http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.8-rc6/
Regards,
Jukka Laitinen
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