linux-kernel - Re: [PATCH 1/5] regulator: core: Resolve supply earlier

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Date:	Mon, 11 Apr 2016 11:59:02 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Thierry Reding <thierry.reding@...il.com>,
	Mark Brown <broonie@...nel.org>
CC:	Liam Girdwood <lgirdwood@...il.com>,
	<linux-kernel@...r.kernel.org>,
	Javier Martinez Canillas <javier@....samsung.com>
Subject: Re: [PATCH 1/5] regulator: core: Resolve supply earlier

Hi Thierry,

On 07/04/16 15:22, Thierry Reding wrote:
> From: Thierry Reding <treding@...dia.com>
> 
> Subsequent patches will need access to the parent supply from within the
> set_machine_constraints() function to properly implement bypass mode. If
> the parent supply hasn't been resolved by that time the voltage can't be
> queried.
> 
> Also, by making sure the supply is resolved early most of the changes in
> set_machine_constraints() don't have to be undone if resolution fails.
> 
> Suggested-by: Mark Brown <broonie@...nel.org>
> Signed-off-by: Thierry Reding <treding@...dia.com>
> ---
>  drivers/regulator/core.c | 27 +++++++++++++++++++++------
>  1 file changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
> index 2786d251b1cc..cc0333a79924 100644
> --- a/drivers/regulator/core.c
> +++ b/drivers/regulator/core.c
> @@ -3972,18 +3972,27 @@ regulator_register(const struct regulator_desc *regulator_desc,
>  
>  	dev_set_drvdata(&rdev->dev, rdev);
>  
> +	if (init_data && init_data->supply_regulator)
> +		rdev->supply_name = init_data->supply_regulator;
> +	else if (regulator_desc->supply_name)
> +		rdev->supply_name = regulator_desc->supply_name;
> +
> +	/*
> +	 * set_machine_constraints() needs the supply to be resolved in order
> +	 * to support querying the current voltage in bypass mode. Resolve it
> +	 * here to more easily handle deferred probing.
> +	 */
> +	ret = regulator_resolve_supply(rdev);
> +	if (ret < 0)
> +		goto scrub;
> +

Thanks for sending this. However, I think that calling
regulator_resolve_supply() can cause a deadlock, because the
regulator_list_mutex is held at this point and
regulator_resolve_supply() calls regulator_dev_lookup() which may try to
request the mutex again.

So may be we need to move this call after the call to
regulator_of_get_init_data() before we acquire the mutex.

Also, if we add this call, then I am wondering if we still need ...

	class_for_each_device(&regulator_class, NULL, NULL,
			      regulator_register_resolve_supply);

Cheers
Jon