On Mon, 29 Jun 2009 00:08:59 +0200 Janusz Krzysztofik <jkrzyszt@xxxxxxxxxxxx> wrote: > AFAIK, both CSSA_L and CDSA_L DMA registers are static. Loaded by CPU > with 16 LSB of initial source and destination port addresses > respectively, they are never updated by the DMA engine itself. That's > why they can't be used for transfer progress indication unless > updated by CPU. > > The old omap-alsa driver was just updating them, intentionally or > not, by reprogramming and restarting DMA every PCM period. That's why > calculating PCM pointers from CSSA_L/CDSA_L worked. > Thanks for finding out this. Good to know that OMAP low-level DMA code now in this respect is as good as HW allows it. > ASoC OMAP driver transfers whole PCM buffer with single DMA transfer, > so it doesn't need to update DMA source/destination port address > after initial playback/capture setup, even if restarting DMA, and > actually never does this. Calculating PCM pointers from CSSA_L/CDSA_L > registers without updating them every period would then be wrong. > > For capture, reading CPC, that follows destination port address > progress, just works fine (for both old and new driver). For > playback, similar hardware functionality seems to be missing, so it > has to be emulated in software if required. > Kind an odd HW behaviour but that can happen. Probably it would be good to explain this also in function omap_get_dma_src_pos. Mark, I think this is fair to queue a fix for 2.6.31. Acked-by: Jarkko Nikula <jhnikula@xxxxxxxxx> -- 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
