linux-kernel - [PATCH v3] dmaengine: rcar-dmac: use TCRB instead of TCR for residue

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Message-ID: <87bml4c5e0.wl%kuninori.morimoto.gx@renesas.com>
Date:   Thu, 19 Oct 2017 01:15:13 +0000
From:   Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Vinod Koul <vinod.koul@...el.com>
Cc:     Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>, dmaengine@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@...esas.com>
Subject: [PATCH v3] dmaengine: rcar-dmac: use TCRB instead of TCR for residue

From: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@...esas.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@...esas.com>
[Kuninori: added detail information in log]
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
---
v2 -> v3

 - Code is back to same as v1
 - log has more detail explanation
 - From: is back to Yokoyama-san again

 drivers/dma/sh/rcar-dmac.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index 2b2c7db..50c4950 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -1310,7 +1310,7 @@ static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan,
 	}

 	/* Add the residue for the current chunk. */
-	residue += rcar_dmac_chan_read(chan, RCAR_DMATCR) << desc->xfer_shift;
+	residue += rcar_dmac_chan_read(chan, RCAR_DMATCRB) << desc->xfer_shift;

 	return residue;
 }
-- 
1.9.1