linux-kernel - Re: [PATCH 2/2] mfd: mfd-core: Honour Device Tree's request to disable a child-device

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Date:   Fri, 18 Oct 2019 17:21:35 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Lee Jones <lee.jones@...aro.org>, broonie@...nel.org,
        linus.walleij@...aro.org, daniel.thompson@...aro.org, arnd@...db.de
Cc:     baohua@...nel.org, stephan@...hold.net,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] mfd: mfd-core: Honour Device Tree's request to
 disable a child-device

On 18/10/2019 13:26, Lee Jones wrote:
> Until now, MFD has assumed all child devices passed to it (via
> mfd_cells) are to be registered.  It does not take into account
> requests from Device Tree and the like to disable child devices
> on a per-platform basis.
> 
> Well now it does.
> 
> Reported-by: Barry Song <Baohua.Song@....com>
> Reported-by: Stephan Gerhold <stephan@...hold.net>
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>   drivers/mfd/mfd-core.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> index eafdadd58e8b..24c139633524 100644
> --- a/drivers/mfd/mfd-core.c
> +++ b/drivers/mfd/mfd-core.c
> @@ -182,6 +182,11 @@ static int mfd_add_device(struct device *parent, int id,
>   	if (parent->of_node && cell->of_compatible) {
>   		for_each_child_of_node(parent->of_node, np) {
>   			if (of_device_is_compatible(np, cell->of_compatible)) {
> +				if (!of_device_is_available(np)) {
> +					/* Ignore disabled devices error free */
> +					ret = 0;
> +					goto fail_alias;
> +				}

Is it possible for a device to have multiple children of the same type? 
If so, it seems like this might not work as desired if, say, the first 
child was disabled but subsequent ones weren't.

It might make sense to use for_each_available_child_of_node() for the 
outer loop, then check afterwards if anything was found.

Robin.

>   				pdev->dev.of_node = np;
>   				pdev->dev.fwnode = &np->fwnode;
>   				break;
>