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Date: Mon, 29 Jun 2009 09:04:03 +0300 From: Jarkko Nikula <jhnikula@...il.com> To: Janusz Krzysztofik <jkrzyszt@....icnet.pl> Cc: Peter Ujfalusi <peter.ujfalusi@...ia.com>, Tony Lindgren <tony@...mide.com>, "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>, "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>, linux-kernel@...r.kernel.org, broonie@...nsource.wolfsonmicro.com Subject: Re: [PATCH] [RFC] ASoC: OMAP: fix OMAP1510 broken PCM pointer callback On Mon, 29 Jun 2009 00:08:59 +0200 Janusz Krzysztofik <jkrzyszt@....icnet.pl> 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@...il.com> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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