Re: [PATCH] i2c: mv64xxx: Fix random system lock caused by runtime PM

[Wolfram Sang <wsa@kernel.org>]

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On Thu, Apr 08, 2021 at 04:00:00AM +0200, Marek Behún wrote:
> I noticed a weird bug with this driver on Marvell CN9130 Customer
> Reference Board.
> 
> Sometime after boot, the system locks with the following message:
>  [104.071363] i2c i2c-0: mv64xxx: I2C bus locked, block: 1, time_left: 0
> 
> The system does not respond afterwards, only warns about RCU stalls.
> 
> This first appeared with commit e5c02cf54154 ("i2c: mv64xxx: Add runtime
> PM support").
> 
> With further experimentation I discovered that adding a delay into
> mv64xxx_i2c_hw_init() fixes this issue. This function is called before
> every xfer, due to how runtime PM works in this driver. It seems that in
> order to work correctly, a delay is needed after the bus is reset in
> this function.
> 
> Since there already is a known erratum with this controller needing a
> delay, I assume that this is just another place this needs to be
> applied. Therefore I apply the delay only if errata_delay is true.
> 
> Signed-off-by: Marek Behún <kabel@kernel.org>

Gregory? Looks reasonable to me and if so, we should have this in 5.12
already. Comments from others are welcome, too, of course.

> ---
>  drivers/i2c/busses/i2c-mv64xxx.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-mv64xxx.c b/drivers/i2c/busses/i2c-mv64xxx.c
> index c590d36b5fd1..5c8e94b6cdb5 100644
> --- a/drivers/i2c/busses/i2c-mv64xxx.c
> +++ b/drivers/i2c/busses/i2c-mv64xxx.c
> @@ -221,6 +221,10 @@ mv64xxx_i2c_hw_init(struct mv64xxx_i2c_data *drv_data)
>  	writel(0, drv_data->reg_base + drv_data->reg_offsets.ext_addr);
>  	writel(MV64XXX_I2C_REG_CONTROL_TWSIEN | MV64XXX_I2C_REG_CONTROL_STOP,
>  		drv_data->reg_base + drv_data->reg_offsets.control);
> +
> +	if (drv_data->errata_delay)
> +		udelay(5);
> +
>  	drv_data->state = MV64XXX_I2C_STATE_IDLE;
>  }
>  
> -- 
> 2.26.2
> 

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