On Wed, Jul 25, 2018 at 10:29 AM Yoshihiro Shimoda
<yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote:
> rcar_dmac_chan_get_residue() should not stop the DMAC, because
> the commit 538603c6026c ("dmaengine: sh: rcar-dmac: avoid to write
> CHCR.TE to 1 if TCR is set to 0") had fixed unexpected re-transferring
> issue. But it had caused the next issue which might stop the cyclic
> mode transferring. Thus, for example R-Car sound might be stopped
> suddenly.
>
> According to the commit 73a47bd0da66 ("dmaengine: rcar-dmac: use TCRB
> instead of TCR for residue"), the purpose of clearing CHCR.DE bit is
> flushing buffered data to calculate the exact residue.
>
> Such the "exact" residue had been required by sh-sci driver. sh-sci
> driver is calling dmaengine_pause() to stop transferring, and get
> "exact" residue. Otherwise, it might receive extra data during
> getting residue without pausing.
>
> In rx_timer_fn() of sh-sci driver:
> dmaengine_tx_status(); /* For checking roughly */
> dmaengine_pause();
> dmaengine_tx_status(); /* For getting residue */
> dmaengine_terminate_all();
>
> But, unfortunately the rcar-dmac driver didn't support dmaengine_pause()
> at that time. So, the sh-sci driver cannot get the "exact" residue
> without stopping the transferring, because rcar-dmac is buffering data
> inside.
>
> Because of these backgrounds, rcar-dmac had been cleared/set CHCR.DE
> bit in rcar_dmac_chan_get_residue() to synchronizing data and getting
> "exact" residue.
>
> However, rcar-dmac driver has rcar_dmac_chan_pause() now, and clearing
> CHCR.DE bit in rcar_dmac_chan_get_residue() doesn't need anymore.
> So, this patch removes the rcar_dmac_sync_tcr().
>
> Fixes: 73a47bd0da66 ("dmaengine: rcar-dmac: use TCRB instead of TCR for residue")
> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> Tested-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@xxxxxxxxxxx>
Makes sense, so
Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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
