[alsa-devel] [RFC] ALSA: add new alsa control byte extended

[Takashi Iwai]

At Fri, 29 Nov 2013 09:59:57 +0530,
Vinod Koul wrote:
> 
> As discussed in the last Audio uConf we need to improve byte controls to allow
> larger size data to be sent to DSPs  The modern DSPs require alsa byte controls
> size which far exceeds the today 512bytes limit. In order for usermode to send
> larger sizes (few 100s of KBs) along with size information we add extended byte
> control interface which sends any size bytes parameter buffer for DSPs to use
> Obviosly the size must be supported by the device and would be required to
> inform the max size allowed for the control.

My primary question is -- must this be a control element?
Why it can't be implemented in hwdep, for example?  In the past, we
already implemented DSP firmware loader in the hwdep side.  It's a bit
complicated (and limited) for a few driver usages, but it was more or
less standardized for them.

My concern extending control element is that it'd need the rewrite in
the whole control API in user-space side, too.  alsactl accesses the
whole control elements and save/restore them, for example.

Also, sharing scalar data and a reference pointer in the same union is
a bit error-prone.


Takashi

> 
> Signed-off-by: Vinod Koul <vinod.koul at intel.com>
> ---
>  include/uapi/sound/asound.h |    8 +++++++-
>  1 files changed, 7 insertions(+), 1 deletions(-)
> 
> diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
> index 9fc6219..8c10359 100644
> --- a/include/uapi/sound/asound.h
> +++ b/include/uapi/sound/asound.h
> @@ -782,7 +782,8 @@ typedef int __bitwise snd_ctl_elem_type_t;
>  #define	SNDRV_CTL_ELEM_TYPE_BYTES	((__force snd_ctl_elem_type_t) 4) /* byte array */
>  #define	SNDRV_CTL_ELEM_TYPE_IEC958	((__force snd_ctl_elem_type_t) 5) /* IEC958 (S/PDIF) setup */
>  #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
> +#define SNDRV_CTL_ELEM_TYPE_BYTES_EXT	((__force snd_ctl_elem_type_t) 7) /* bytes array extended */
> +#define	SNDRV_CTL_ELEM_TYPE_LAST	SNDRV_CTL_ELEM_TYPE_BYTES_EXT
>  
>  typedef int __bitwise snd_ctl_elem_iface_t;
>  #define	SNDRV_CTL_ELEM_IFACE_CARD	((__force snd_ctl_elem_iface_t) 0) /* global control */
> @@ -891,6 +892,11 @@ struct snd_ctl_elem_value {
>  			unsigned char data[512];
>  			unsigned char *data_ptr;	/* obsoleted */
>  		} bytes;
> +		struct {
> +			unsigned long size;	/* size of buffer */
> +			__u64 data;	i	/* user data pointer */
> +		} bytes_ext;
> +
>  		struct snd_aes_iec958 iec958;
>  	} value;		/* RO */
>  	struct timespec tstamp;
> -- 
> 1.7.0.4
>