[alsa-devel] [PATCH] ALSA: firewire-lib/fireworks: fix miss detection of received MIDI messages

[Takashi Iwai]

On Mon, 01 Jul 2019 16:23:05 +0200,
Takashi Sakamoto wrote:
> 
> On Mon, Jul 01, 2019 at 04:14:02PM +0200, Takashi Iwai wrote:
> > On Mon, 01 Jul 2019 12:59:27 +0200,
> > Takashi Sakamoto wrote:
> > > 
> > > In IEC 61883-6, 8 MIDI data streams are multiplexed into single
> > > MIDI conformant data channel. The index of stream is calculated by
> > > modulo 8 of the value of data block counter.
> > > 
> > > In fireworks, the value of data block counter in CIP header has a quirk
> > > with firmware version v5.0.0, v5.7.3 and v5.8.0. This brings ALSA
> > > IEC 61883-1/6 packet streaming engine to miss detection of MIDI
> > > messages.
> > > 
> > > This commit fixes the miss detection to modify the value of data block
> > > counter for the modulo calculation.
> > > 
> > > For maintainers, this bug exists since a commit 18f5ed365d3f ("ALSA:
> > > fireworks/firewire-lib: add support for recent firmware quirk") in Linux
> > > kernel v4.2. There're many changes since the commit.  This fix can be
> > > backported to Linux kernel v4.4 or later. I tagged a base commit to the
> > > backport for your convenience.
> > > 
> > > Besides, my work for Linux kernel v5.3 brings heavy code refactoring and
> > > some structure members are renamed in 'sound/firewire/amdtp-stream.h'.
> > > The content of this patch brings conflict when merging -rc tree with
> > > this patch to the latest tree. I request maintainers to solve the
> > > conflict by replacing 'tx_first_dbc' with 'ctx_data.tx.first_dbc'.
> > > 
> > > Fixes: df075feefbd3 ("ALSA: firewire-lib: complete AM824 data block processing layer")
> > > Cc: <stable at vger.kernel.org> # v4.4+
> > > Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>
> > 
> > Thanks, applied.
> 
> Thanks for your application, however I found my mistake in this patch.
> Would you please reset your application if possible?
> 
> diff --git a/sound/firewire/amdtp-am824.c b/sound/firewire/amdtp-am824.c
> index 4210e5c6262e..4d677fcb4fc2 100644
> --- a/sound/firewire/amdtp-am824.c
> +++ b/sound/firewire/amdtp-am824.c
> @@ -321,6 +321,7 @@ static void read_midi_messages(struct amdtp_stream *s,
>         u8 *b;
>  
>         for (f = 0; f < frames; f++) {
> +               port = (8 - s->tx_first_dbc + s->data_block_counter + f) % 8;
>                 port = (s->data_block_counter + f) % 8;
>                 b = (u8 *)&buffer[p->midi_position];
> 
> Just inserting the above line has no meaning itself...

Ah yes.  OK, will reset the repo.  Please resubmit the fix patch.


Takashi