linux-kernel - Re: [PATCH 1/2] misc: atmel_pwm: add deferred-probing support

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Date:	Wed, 30 Oct 2013 12:25:51 +0100
From:	Johan Hovold <jhovold@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	linux-arm-kernel@...ts.infradead.org,
	Johan Hovold <jhovold@...il.com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] misc: atmel_pwm: add deferred-probing support

On Tue, Oct 22, 2013 at 06:32:39PM +0200, Johan Hovold wrote:
> Two drivers (atmel-pwm-bl and leds-atmel-pwm) currently depend on the
> atmel_pwm driver to have bound to any pwm-device before their devices
> are probed.
> 
> Support deferred probing of such devices by making sure to return
> -EPROBE_DEFER from pwm_channel_alloc when no pwm-device has yet been
> bound.
> 
> Signed-off-by: Johan Hovold <jhovold@...il.com>

This patch, 5c6d6fd1 ("misc: atmel_pwm: add deferred-probing support"),
and 9d3fde86 ("backlight: atmel-pwm-bl: fix deferred probe from __init")
in linux-next should probably be considered for inclusion in stable.

Without them the atmel-pwm-bl driver may always fail to probe depending
on link order.

Thanks,
Johan

> ---
>  drivers/misc/atmel_pwm.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/atmel_pwm.c b/drivers/misc/atmel_pwm.c
> index 494d050..a6dc56e 100644
> --- a/drivers/misc/atmel_pwm.c
> +++ b/drivers/misc/atmel_pwm.c
> @@ -90,8 +90,10 @@ int pwm_channel_alloc(int index, struct pwm_channel *ch)
>  	unsigned long	flags;
>  	int		status = 0;
>  
> -	/* insist on PWM init, with this signal pinned out */
> -	if (!pwm || !(pwm->mask & 1 << index))
> +	if (!pwm)
> +		return -EPROBE_DEFER;
> +
> +	if (!(pwm->mask & 1 << index))
>  		return -ENODEV;
>  
>  	if (index < 0 || index >= PWM_NCHAN || !ch)
> -- 
> 1.8.4
> 
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