Re: [Alsa-devel] [linuxsh-dev] [PATCH] Add support for Yamaha AICA sound on SEGA Dreamcast

[Takashi Iwai <tiwai@suse.de>]

At Wed, 07 Jun 2006 19:16:42 +0100,
Adrian McMenamin wrote:
> 
> On Wed, 2006-06-07 at 11:51 +0200, Takashi Iwai wrote:
> > At Wed, 07 Jun 2006 00:10:48 +0100,
> > Adrian McMenamin wrote:
> > > 
> > > On Tue, 2006-06-06 at 12:25 +0200, Takashi Iwai wrote:
> > > 
> > > > Another big concern is that spu_dma_work is initialized/rewritten
> > > > dynamically in spu_begin_dma() and aica_period_elapsed() via
> > > > INIT_WORK() and PREPARE_WOR().  This looks pretty strange and may be
> > > > racy.
> > > 
> > > Actually, the two macros INIT_WORK and PREPARE_WORK use the same work
> > > queue but ask it to schedule the execution of two different (if very
> > > similar) functions start_spu_dma() - which does the initial transfer and
> > > more_spu_dma - which tops up the dma transfers.
> > > 
> > > So I think I've got that right.
> > 
> > What's wrong with using two individual work struct so that you
> > initialize them only once?
> > I wonder it because you already have unused fields work and work2...
> > 
> They've gone actually.
> 
> I need to initialise them because every call is a discrete processing
> job - ie I send one thing to go, then when a period has elapsed I
> schedule another transfer to run on the kernel thread.
> 
> Isn't this the way it is meant to work?

It's uncoventional that a work struct is re-initialized on the fly.

IMO, it's better to introduce a flag indicating the stream is already
running and use a single function/work struct.  For example,

	static void do_first_event(struct stream *str)
	{
		...
		str->running = 1;
	}

	static void do_more_event(struct stream *str)
	{
		...
	}

	static void work_event(void *data)
	{
		struct stream *str = data;

		if (str->running)
			do_more_event(str);
		else
			do_first_event(str);
	}

	trigger_start()
	{
		queue_work(queue, &this_work);
	}

	interrupt_handler()
	{
		...
		queue_work(queue, &this_work);
		...
	}

	initialization()
	{
		...
		queue = create_workqueue("xxx");
		INIT_WORK(&this_work, work_event, str);
		...
	}