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Date: Fri, 25 Sep 2020 22:07:32 +0800
From: Coiby Xu <coiby.xu@...il.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Alex Elder <elder@...aro.org>
Cc: devel@...verdev.osuosl.org,
"moderated list:SOUND" <alsa-devel@...a-project.org>,
Vaibhav Agarwal <vaibhav.sr@...il.com>,
Mark Greer <mgreer@...malcreek.com>,
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: [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@...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 */
>
>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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