[PATCH] power-domain: fix hang in endless loop on i.MX8

[Oliver Graute <oliver.graute@gmail.com>]

On 15/02/20, Anatolij Gustschin wrote:
> Currently when booting the kernel on i.MX8 U-Boot hangs in an
> endless loop when switching off dma, connectivity or lsio power
> domains during device removal. It hapens first when removing
> gpio0 (gpio at 5d080000) device, here its power domain device
> 'lsio_gpio0' is obtained for switching off power. Since the
> obtained 'lsio_gpio0' device is removed afterwards, its power
> domain is also switched off and here the parent power domain
> device 'lsio_power_domain' is optained for switching off the
> power. Thereafter, when the obtained 'lsio_power_domain' is
> removed, device_remove() removes its first child 'lsio_gpio0'.
> During this child removal the 'lsio_power_domain' device is
> obtained again for switching and when removing it later,
> the same child removal is repeated, so we are stuck in an
> endless loop. Below is a snippet from dm tree on i.MX8QXP
> for better illustration of the DM devices relationship:
> 
>  Class     Index  Probed  Driver                Name
> -----------------------------------------------------------
>  root          0  [ + ]   root_driver           root_driver
> ...
>  simple_bus    0  [ + ]   generic_simple_bus    |-- imx8qx-pm
>  power_doma    0  [ + ]   imx8_power_domain     |   |-- lsio_power_domain
>  power_doma    1  [ + ]   imx8_power_domain     |   |   |-- lsio_gpio0
>  power_doma    2  [ + ]   imx8_power_domain     |   |   |-- lsio_gpio1
> 
> Do not remove a power domain device if it is a parent of the
> currently controlled device.
> 
> Fixes: 52edfed65de9 ("dm: core: device: switch off power domain after device removal")
> Signed-off-by: Anatolij Gustschin <agust@denx.de>
> Reported-by: Oliver Graute <oliver.graute@gmail.com>
> Reported-by: Fabio Estevam <festevam@gmail.com>
> 
> ---
>  drivers/power/domain/power-domain-uclass.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/power/domain/power-domain-uclass.c b/drivers/power/domain/power-domain-uclass.c
> index d9c623b56e..d8fe4d4877 100644
> --- a/drivers/power/domain/power-domain-uclass.c
> +++ b/drivers/power/domain/power-domain-uclass.c
> @@ -127,6 +127,18 @@ static int dev_power_domain_ctrl(struct udevice *dev, bool on)
>  			ret = power_domain_off(&pd);
>  	}
>  
> +	/*
> +	 * For platforms with parent and child power-domain devices
> +	 * we may not run device_remove() on the power-domain parent
> +	 * because it will result in removing its children and switching
> +	 * off their power-domain parent. So we will get here again and
> +	 * again and will be stuck in an endless loop.
> +	 */
> +	if (!on && dev_get_parent(dev) == pd.dev &&
> +	    device_get_uclass_id(dev) == UCLASS_POWER_DOMAIN) {
> +		return ret;
> +	}
> +
>  	/*
>  	 * power_domain_get() bound the device, thus
>  	 * we must remove it again to prevent unbinding
> -- 
> 2.17.1

thx, just tested this and now I can drop my revert mentioned here:

https://lists.denx.de/pipermail/u-boot/2020-February/398910.html

Best regards,

Oliver