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    SubjectRe: [PATCH 3/3] [PATCH] staging: greybus: __u8 is sufficient for snd_ctl_elem_type_t and snd_ctl_elem_iface_t
    On Thu, Sep 24, 2020 at 01:00:57PM +0200, Greg Kroah-Hartman wrote:
    >On Thu, Sep 24, 2020 at 06:20:39PM +0800, Coiby Xu wrote:
    >> Use __8 to replace int and remove the unnecessary __bitwise type attribute.
    >>
    >> Found by sparse,
    >>
    >> $ 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@gmail.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 */
    >
    >I can't take a uapi sound header file patch along with a driver change,
    >these need to be independant.

    Thank you and Alex for reminding me this is a change of public header!
    >
    >And this is a userspace api, you just changed the size of an externally
    >facing variable, are you _SURE_ that is ok to do?

    The reasons I make this change are, 1) using int to represent 7 enumeration
    values seems to be overkill; 2) using one type could avoid worries
    about byte order.

    I examine one userspace example (libalsa-intf/alsa_mixer.c [1]). This
    change won't cause compiling breakage. But I don't the experience to
    imagine any other bad consequence.

    Another way to avoid userspace API change is to let
    "struct gb_audio_ctl_elem_info" use snd_ctl_elem_iface_t type which may
    be more elegant than using "__force" as suggested by Alex,

    $ git diff
    diff --git a/include/linux/greybus/greybus_protocols.h b/include/linux/greybus/greybus_protocols.h
    index aeb8f9243545..7f6753ec7ef7 100644
    --- a/include/linux/greybus/greybus_protocols.h
    +++ b/include/linux/greybus/greybus_protocols.h
    @@ -8,6 +8,7 @@
    #define __GREYBUS_PROTOCOLS_H

    #include <linux/types.h>
    +#include <sound/asound.h>

    /* Fixed IDs for control/svc protocols */

    @@ -1997,7 +1998,7 @@ struct gb_audio_enumerated {
    } __packed;

    struct gb_audio_ctl_elem_info { /* See snd_ctl_elem_info in Linux source */
    - __u8 type; /* GB_AUDIO_CTL_ELEM_TYPE_* */
    + snd_ctl_elem_type_t type; /* GB_AUDIO_CTL_ELEM_TYPE_* */
    __le16 dimen[4];
    union {
    struct gb_audio_integer integer
    My only concern is if greybus authors have any special reason to not include
    sound/asound.h in the first place and re-define things like SNDRV_CTL_ELEM_TYPE_*,

    /* See SNDRV_CTL_ELEM_TYPE_* in Linux source */
    #define GB_AUDIO_CTL_ELEM_TYPE_BOOLEAN 0x01
    #define GB_AUDIO_CTL_ELEM_TYPE_INTEGER 0x02
    /* See SNDRV_CTL_ELEM_IFACE_* in Linux source */
    #define GB_AUDIO_CTL_ELEM_IFACE_CARD 0x00
    ...
    /* SNDRV_CTL_ELEM_ACCESS_* in Linux source */
    #define GB_AUDIO_ACCESS_READ BIT(0)
    ...
    [1] https://gitlab.com/Codeaurora/platform_hardware_qcom_audio/-/blob/aee6032826ec7c8b6edda404422fda0ef40ec2db/libalsa-intf/alsa_mixer.c
    alsa_mixer.c
    >
    >thanks,
    >
    >greg k-h

    --
    Best regards,
    Coiby

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