On 09/12/2012 03:00 PM, Russell King - ARM Linux wrote: > On Wed, Sep 12, 2012 at 02:47:07PM +0300, Peter Ujfalusi wrote: >> 2. Pause/Resume >> OMAP DMA engine backend does not support pausing and resuming >> an in-progress transfer. It is unclear from the specs what >> effect clearing the enable bit has on the DMA position of a >> destination synchronized transfer, and whether the transfer >> can be restarted from the exact point that it was paused (or >> whether the data in the FIFO read from memory is simply >> discarded.) > > It's worth noting that this comment (which was in my original patch) > is there to spark _comment_ and _discussion_ and should not make its > way into the final version of these patches. > > Given that suspend/resume is important on OMAP platforms, it's something > that needs to be resolved - in a way that complies with what ALSA expects. > I do not believe that the way the existing drivers do this is compliant > as the manuals imply that stopping memory->peripheral transfers results > in data being discarded from the DMA's FIFOs. As I understand it, ALSA > requires no data to be discarded. > > As we have no way to know how much data may be discarded from the DMA > FIFO... I need to look at this, but at first look we do wait for the drain in omap_stop_dma(). We used to use omap_stop_dma/omap_start_dma for pause/resume operations. But sDMA also have a bit: CDPi: PAUSE_LINK_LIST which should do what we are looking for. Need to read the relevant parts of the TRM, but AFAIK we are using normal mode with linked list (self linking). I already have the patch for this, I just need to test it on HW. -- Péter -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
