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

[Neil Armstrong]

Hi,

On 17/02/2020 10:07, Oliver Graute wrote:
> 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 at denx.de>
>> Reported-by: Oliver Graute <oliver.graute at gmail.com>
>> Reported-by: Fabio Estevam <festevam at 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

The revert is still needed... it breaks multiple amlogic boards and the fix
is not as simple as this one.

Neil

> 
> Best regards,
> 
> Oliver
>