Re: [Alsa-devel] Re: [linuxsh-dev] [PATCH] ALSA driver for Yamaa AICA on Sega Dreamcast

[Adrian McMenamin <adrian@mcmen.demon.co.uk>]

On Mon, 2006-04-17 at 04:29 +0300, Paul Mundt wrote:
> A few quick comments.. though looking at the earlier thread, most of
> these were already pointed out..
> 

> 
> You can't be serious, you're trying to setup, transfer, and wait for
> completion for a DMA transfer while holding a spinlock? The fact this
> hasn't blown up on you is sheer luck. Use dma_wait_for_completion(), it
> does the right thing.
> 
> Additionaly you need a timeout here if you were for some reason intent on
> doing this while working against the DMA subsystem, if your DMA gets
> stuck this will blow up.
> 

As I wrote last week dma_wait_for_completion won't hack G2 DMA:


147 void dma_wait_for_completion(unsigned int chan)
148 {
149         struct dma_info *info = get_dma_info(chan);
150         struct dma_channel *channel = &info->channels[chan];
151 
152         if (channel->flags & DMA_TEI_CAPABLE) {
153                 wait_event(channel->wait_queue,
154                            (info->ops->get_residue(channel) == 0));
155                 return;
156         }
157 
158         while (info->ops->get_residue(channel))
159                 cpu_relax();
160 }

get_residue never returns 0 for G2 DMA. When the dma is complete get_residue returns the size of the total transfer. Therefore I've no choice but to write my own handler (spinlocks question aside).