[PATCH] i2c: aspeed: Fix i2c bus hang in slave read

[Joel Stanley]

On Thu, 10 Aug 2023 at 07:22, Jian Zhang <zhangjian.3032 at bytedance.com> wrote:
>
> When the `CONFIG_I2C_SLAVE` option is enabled and the device operates
> as a slave, a situation arises where the master sends a START signal
> without the accompanying STOP signal. This action results in a
> persistent I2C bus timeout. The core issue stems from the fact that
> the i2c controller remains in a slave read state without a timeout
> mechanism. As a consequence, the bus perpetually experiences timeouts.
>
> This proposed patch addresses this problem by introducing a status
> check during i2c transmit timeouts. In the event that the controller
> is in a slave read state, the i2c controller will be reset to restore
> proper functionality and allow the I2C bus to resume normal operation.
>
> Signed-off-by: Jian Zhang <zhangjian.3032 at bytedance.com>

Tommy has submitted a similar fix:

 https://lore.kernel.org/linux-i2c/20230906004910.4157305-1-tommy_huang@aspeedtech.com/

His change is very heavy handed; it reinitialises the bus including
re-parsing the device tree (!).

Should we have merged this fix instead? If not, are you able to
confirm that his change fixes your issue?

Cheers,

Joel

> ---
>  drivers/i2c/busses/i2c-aspeed.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
> index e76befe3f60f..1a95205fc946 100644
> --- a/drivers/i2c/busses/i2c-aspeed.c
> +++ b/drivers/i2c/busses/i2c-aspeed.c
> @@ -113,6 +113,7 @@
>                  ASPEED_I2CD_M_RX_CMD |                                        \
>                  ASPEED_I2CD_M_TX_CMD |                                        \
>                  ASPEED_I2CD_M_START_CMD)
> +#define ASPEED_I2CD_SLAVE_CMDS_MASK                    GENMASK(31, 29)
>
>  /* 0x18 : I2CD Slave Device Address Register   */
>  #define ASPEED_I2CD_DEV_ADDR_MASK                      GENMASK(6, 0)
> @@ -706,6 +707,22 @@ static int aspeed_i2c_master_xfer(struct i2c_adapter *adap,
>                      ASPEED_I2CD_BUS_BUSY_STS))
>                         aspeed_i2c_recover_bus(bus);
>
> +#if IS_ENABLED(CONFIG_I2C_SLAVE)
> +               /*
> +                * If master timed out and bus is in slave mode.
> +                * reset the slave mode.
> +                */
> +               if (readl(bus->base + ASPEED_I2C_CMD_REG) & ASPEED_I2CD_SLAVE_CMDS_MASK) {
> +                       spin_lock_irqsave(&bus->lock, flags);
> +                       u32 func_ctrl_reg_val = readl(bus->base + ASPEED_I2C_FUN_CTRL_REG);
> +
> +                       writel(0, bus->base + ASPEED_I2C_FUN_CTRL_REG);
> +                       writel(func_ctrl_reg_val, bus->base + ASPEED_I2C_FUN_CTRL_REG);
> +                       bus->slave_state = ASPEED_I2C_SLAVE_INACTIVE;
> +                       spin_unlock_irqrestore(&bus->lock, flags);
> +               }
> +#endif
> +
>                 /*
>                  * If timed out and the state is still pending, drop the pending
>                  * master command.
> --
> 2.30.2
>