linux-kernel - Re: [PATCH 1/2] mfd: mfd-core: Add mechanism for removal of a subset of children

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Date:   Wed, 13 May 2020 10:18:49 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     <lee.jones@...aro.org>
CC:     <broonie@...nel.org>, <patches@...nsource.cirrus.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mfd: mfd-core: Add mechanism for removal of a subset
 of children

On Mon, May 11, 2020 at 04:53:32PM +0100, Charles Keepax wrote:
> Currently, the only way to remove MFD children is with a call to
> mfd_remove_devices, which will remove all the children. Under
> some circumstances it is useful to remove only a subset of the
> child devices. For example if some additional clean up is required
> between removal of certain child devices.
> 
> To accomplish this a tag field is added to mfd_cell, and a
> corresponding mfd_remove_devices_by_tag function is added to
> remove children with a specific tag. This allows a good amount of
> flexibility in which child devices a driver wishes to remove, as a
> driver could target specific drivers or a large group. Allowing other
> use-cases such as removing drivers for functionality that is no longer
> required.
> 
> Some investigation was done of using the mfd_cell name and id fields,
> but it is hard to achieve a good level of flexibility there, at least
> without significant complexity. Since the id gets modified by the core
> and can even by automatically generated. Using the name alone would
> work for my usecase but it is not hard to imagine a situation where it
> wouldn't.
> 
> Signed-off-by: Charles Keepax <ckeepax@...nsource.cirrus.com>
> ---
> 
> Following on from our discussions here:
> 
> https://lore.kernel.org/lkml/20200122110842.10702-2-ckeepax@opensource.cirrus.com/#t
> 
> Happy to discuss other approaches as well, but this one was quite
> appealing as it was very simple but affords quite a lot of flexibility.
> 
> Thanks,
> Charles
> 
> 
>  drivers/mfd/mfd-core.c   | 11 +++++++++++
>  include/linux/mfd/core.h |  2 ++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> index f5a73af60dd40..83a57186169de 100644
> --- a/drivers/mfd/mfd-core.c
> +++ b/drivers/mfd/mfd-core.c
> @@ -287,6 +287,7 @@ static int mfd_remove_devices_fn(struct device *dev, void *data)
>  {
>  	struct platform_device *pdev;
>  	const struct mfd_cell *cell;
> +	int tag = (int)data;

Yeah as the build bot points out should have actually used a
pointer here. Will update for that if we don't have any major
objections to the approach in general.

Thanks,
Charles