Re: [PATCH] ALSA: seq: Improve UMP SysEx packing

[Takashi Iwai <tiwai@xxxxxxx>]

On Wed, 26 Jun 2024 18:10:15 +0200,
Takashi Iwai wrote:
> 
> The initial implementation of 7bit SysEx message conversion to UMP did
> a trick to deal with the first SysEx start byte (0xf7).  The converter
> trims it and sends the first packet with the content of 5 bytes.
> Although this is valid and should work, it's not ideal and a bit
> confusing as if something goes wrong.
> 
> This patch improves the handling to try filling always 6 bytes in the
> package.
> 
> Fixes: e9e02819a98a ("ALSA: seq: Automatic conversion of UMP events")
> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>

Scratch this one.  It won't work properly when the sysex message is
split.  Will rework on it.


Takashi

> ---
>  sound/core/seq/seq_ump_convert.c | 48 +++++++++++++++++++-------------
>  1 file changed, 28 insertions(+), 20 deletions(-)
> 
> diff --git a/sound/core/seq/seq_ump_convert.c b/sound/core/seq/seq_ump_convert.c
> index e90b27a135e6..952e64c499dd 100644
> --- a/sound/core/seq/seq_ump_convert.c
> +++ b/sound/core/seq/seq_ump_convert.c
> @@ -1192,7 +1192,7 @@ static int cvt_sysex_to_ump(struct snd_seq_client *dest,
>  {
>  	struct snd_seq_ump_event ev_cvt;
>  	unsigned char status;
> -	u8 buf[6], *xbuf;
> +	u8 buf[6];
>  	int offset = 0;
>  	int len, err;
>  
> @@ -1200,36 +1200,44 @@ static int cvt_sysex_to_ump(struct snd_seq_client *dest,
>  		return 0;
>  
>  	setup_ump_event(&ev_cvt, event);
> +	len = 0;
> +	status = UMP_SYSEX_STATUS_START;
>  	for (;;) {
> -		len = snd_seq_expand_var_event_at(event, sizeof(buf), buf, offset);
> -		if (len <= 0)
> +		err = snd_seq_expand_var_event_at(event, sizeof(buf) - len,
> +						  buf + len, offset);
> +		if (err < 0)
> +			break;
> +		len += err;
> +		if (!len)
>  			break;
>  		if (WARN_ON(len > 6))
>  			break;
> -		offset += len;
> -		xbuf = buf;
> -		if (*xbuf == UMP_MIDI1_MSG_SYSEX_START) {
> -			status = UMP_SYSEX_STATUS_START;
> -			xbuf++;
> +		offset += err;
> +		if (status == UMP_SYSEX_STATUS_START &&
> +		    buf[0] == UMP_MIDI1_MSG_SYSEX_START) {
>  			len--;
> -			if (len > 0 && xbuf[len - 1] == UMP_MIDI1_MSG_SYSEX_END) {
> -				status = UMP_SYSEX_STATUS_SINGLE;
> -				len--;
> -			}
> -		} else {
> -			if (xbuf[len - 1] == UMP_MIDI1_MSG_SYSEX_END) {
> -				status = UMP_SYSEX_STATUS_END;
> -				len--;
> -			} else {
> -				status = UMP_SYSEX_STATUS_CONTINUE;
> -			}
> +			memmove(buf, buf + 1, len);
> +			continue; /* fill one more byte */
>  		}
> -		fill_sysex7_ump(dest_port, ev_cvt.ump, status, xbuf, len);
> +		if (buf[len - 1] == UMP_MIDI1_MSG_SYSEX_END) {
> +			len--;
> +			if (status == UMP_SYSEX_STATUS_START)
> +				status = UMP_SYSEX_STATUS_SINGLE;
> +			else
> +				status = UMP_SYSEX_STATUS_END;
> +		}
> +		fill_sysex7_ump(dest_port, ev_cvt.ump, status, buf, len);
>  		err = __snd_seq_deliver_single_event(dest, dest_port,
>  						     (struct snd_seq_event *)&ev_cvt,
>  						     atomic, hop);
>  		if (err < 0)
>  			return err;
> +
> +		if (status == UMP_SYSEX_STATUS_START)
> +			status = UMP_SYSEX_STATUS_CONTINUE;
> +		else if (status != UMP_SYSEX_STATUS_CONTINUE)
> +			break;
> +		len = 0; /* reset filling */
>  	}
>  	return 0;
>  }
> -- 
> 2.43.0
>