Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Thu, 19 Oct 2017 09:41:03 +0200 | Subject | Re: [PATCH v3] dmaengine: rcar-dmac: use TCRB instead of TCR for residue |
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On Thu, Oct 19, 2017 at 3:15 AM, Kuninori Morimoto <kuninori.morimoto.gx@renesas.com> wrote: > From: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com> > > SYS/RT/Audio DMAC includes independent data buffers for reading > and writing. Therefore, the read transfer counter and write transfer > counter have different values. > TCR indicates read counter, and TCRB indicates write counter. > The relationship is like below. > > TCR TCRB > [SOURCE] -> [DMAC] -> [SINK] > > In the MEM_TO_DEV direction, what really matters is how much data has > been written to the device. If the DMA is interrupted between read and > write, then, the data doesn't end up in the destination, so shouldn't > be counted. TCRB is thus the register we should use in this cases. > > In the DEV_TO_MEM direction, the situation is more complex. Both the > read and write side are important. What matters from a data consumer > point of view is how much data has been written to memory. > On the other hand, if the transfer is interrupted between read and > write, we'll end up losing data. It can also be important to report. > > In the MEM_TO_MEM direction, what matters is of course how much data > has been written to memory from data consumer point of view. > Here, because read and write have independent data buffers, it will > take a while for TCR and TCRB to become equal. Thus we should check > TCRB in this case, too. > > Thus, all cases we should check TCRB instead of TCR. > > Without this patch, Sound Capture has noise after PluseAudio support > (= 07b7acb51d2 ("ASoC: rsnd: update pointer more accurate")), because > the recorder will use wrong residue counter which indicates transferred > from sound device, but in reality the data was not yet put to memory > and recorder will record it. > > Signed-off-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com> > [Kuninori: added detail information in log] > Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com> > --- > v2 -> v3 > > - Code is back to same as v1 > - log has more detail explanation > - From: is back to Yokoyama-san again
Thanks for the update!
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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