At Wed, 12 Sep 2012 13:00:28 +0100, 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. I agree this can be regarded as a sort of regression... > 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. ... but in general you don't need to implement the full PAUSE and RESUME operations for PCM. For example, when SNDRV_PCM_INFO_RESUME bit isn't set, user-space is supposed to do a clean restart of the stream at wake up. So, it shouldn't break the apps severely in theory (but in practice, who knows :) > As we have no way to know how much data may be discarded from the DMA > FIFO... Yeah, the FIFO and the amount of other on flight data can be better managed. Takashi -- 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
