linux-kernel - Re: [greybus-dev] [PATCH 3/3] [PATCH] staging: greybus: __u8 is sufficient for snd_ctl_elem_type_t and snd_ctl_elem_iface

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Date:   Thu, 24 Sep 2020 08:01:09 -0500
From:   Alex Elder <elder@...aro.org>
To:     Coiby Xu <coiby.xu@...il.com>, devel@...verdev.osuosl.org
Cc:     "moderated list:SOUND" <alsa-devel@...a-project.org>,
        Alex Elder <elder@...nel.org>, Takashi Iwai <tiwai@...e.com>,
        Johan Hovold <johan@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        "moderated list:GREYBUS SUBSYSTEM" <greybus-dev@...ts.linaro.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [greybus-dev] [PATCH 3/3] [PATCH] staging: greybus: __u8 is
 sufficient for snd_ctl_elem_type_t and snd_ctl_elem_iface_t

On 9/24/20 5:20 AM, Coiby Xu wrote:
> Use __8 to replace int and remove the unnecessary __bitwise type attribute.
> 
> Found by sparse,

Greg's right, don't change the public header.

You could try this in the Greybus code to eliminate the warning,
but I haven't tried it (and for all I know it's not a good idea):

	uinfo->type = (__force snd_ctl_elem_type_t)info->type;

					-Alex

> $ make C=2 drivers/staging/greybus/
> drivers/staging/greybus/audio_topology.c:185:24: warning: cast to restricted snd_ctl_elem_type_t
> drivers/staging/greybus/audio_topology.c:679:14: warning: restricted snd_ctl_elem_iface_t degrades to integer
> drivers/staging/greybus/audio_topology.c:906:14: warning: restricted snd_ctl_elem_iface_t degrades to integer
> 
> Signed-off-by: Coiby Xu <coiby.xu@...il.com>
> ---
>  drivers/staging/greybus/audio_topology.c | 2 +-
>  include/uapi/sound/asound.h              | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/greybus/audio_topology.c b/drivers/staging/greybus/audio_topology.c
> index 56bf1a4f95ad..f6023ff390c2 100644
> --- a/drivers/staging/greybus/audio_topology.c
> +++ b/drivers/staging/greybus/audio_topology.c
> @@ -182,7 +182,7 @@ static int gbcodec_mixer_ctl_info(struct snd_kcontrol *kcontrol,
>  	/* update uinfo */
>  	uinfo->access = data->access;
>  	uinfo->count = data->vcount;
> -	uinfo->type = (snd_ctl_elem_type_t)info->type;
> +	uinfo->type = info->type;
>  
>  	switch (info->type) {
>  	case GB_AUDIO_CTL_ELEM_TYPE_BOOLEAN:
> diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
> index 535a7229e1d9..8e71a95644ab 100644
> --- a/include/uapi/sound/asound.h
> +++ b/include/uapi/sound/asound.h
> @@ -950,7 +950,7 @@ struct snd_ctl_card_info {
>  	unsigned char components[128];	/* card components / fine identification, delimited with one space (AC97 etc..) */
>  };
>  
> -typedef int __bitwise snd_ctl_elem_type_t;
> +typedef __u8 snd_ctl_elem_type_t;
>  #define	SNDRV_CTL_ELEM_TYPE_NONE	((__force snd_ctl_elem_type_t) 0) /* invalid */
>  #define	SNDRV_CTL_ELEM_TYPE_BOOLEAN	((__force snd_ctl_elem_type_t) 1) /* boolean type */
>  #define	SNDRV_CTL_ELEM_TYPE_INTEGER	((__force snd_ctl_elem_type_t) 2) /* integer type */
> @@ -960,7 +960,7 @@ typedef int __bitwise snd_ctl_elem_type_t;
>  #define	SNDRV_CTL_ELEM_TYPE_INTEGER64	((__force snd_ctl_elem_type_t) 6) /* 64-bit integer type */
>  #define	SNDRV_CTL_ELEM_TYPE_LAST	SNDRV_CTL_ELEM_TYPE_INTEGER64
>  
> -typedef int __bitwise snd_ctl_elem_iface_t;
> +typedef __u8 snd_ctl_elem_iface_t;
>  #define	SNDRV_CTL_ELEM_IFACE_CARD	((__force snd_ctl_elem_iface_t) 0) /* global control */
>  #define	SNDRV_CTL_ELEM_IFACE_HWDEP	((__force snd_ctl_elem_iface_t) 1) /* hardware dependent device */
>  #define	SNDRV_CTL_ELEM_IFACE_MIXER	((__force snd_ctl_elem_iface_t) 2) /* virtual mixer device */
>