[PATCH 6/7] dmaengine: ste_dma40: don't allow high priority dest event lines

[Fabio Baltieri]

From: Rabin Vincent <rabin.vincent@xxxxxxxxxxxxxx>

Hardware bug: when a logical channel is triggerred by a high priority
destination event line, an extra packet transaction is generated in case
of important data write response latency on previous logical channel A
and if the source transfer of current logical channel B is already
completed and if no other channel with a higher priority than B is
waiting for execution.

Software workaround: do not set the high priority level for the
destination event lines that trigger logical channels.

Signed-off-by: Rabin Vincent <rabin.vincent@xxxxxxxxxxxxxx>
Reviewed-by: Shreshtha Kumar Sahu <shreshthakumar.sahu@xxxxxxxxxxxxxx>
Acked-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Signed-off-by: Fabio Baltieri <fabio.baltieri@xxxxxxxxxx>
---
 drivers/dma/ste_dma40.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c
index d8d58d9..f871df6 100644
--- a/drivers/dma/ste_dma40.c
+++ b/drivers/dma/ste_dma40.c
@@ -2181,11 +2181,24 @@ static void __d40_set_prio_rt(struct d40_chan *d40c, int dev_type, bool src)
 {
 	bool realtime = d40c->dma_cfg.realtime;
 	bool highprio = d40c->dma_cfg.high_priority;
-	u32 prioreg = highprio ? D40_DREG_PSEG1 : D40_DREG_PCEG1;
 	u32 rtreg = realtime ? D40_DREG_RSEG1 : D40_DREG_RCEG1;
 	u32 event = D40_TYPE_TO_EVENT(dev_type);
 	u32 group = D40_TYPE_TO_GROUP(dev_type);
 	u32 bit = 1 << event;
+	u32 prioreg;
+
+	/*
+	 * Due to a hardware bug, in some cases a logical channel triggered by
+	 * a high priority destination event line can generate extra packet
+	 * transactions.
+	 *
+	 * The workaround is to not set the high priority level for the
+	 * destination event lines that trigger logical channels.
+	 */
+	if (!src && chan_is_logical(d40c))
+		highprio = false;
+
+	prioreg = highprio ? D40_DREG_PSEG1 : D40_DREG_PCEG1;
 
 	/* Destination event lines are stored in the upper halfword */
 	if (!src)
-- 
1.7.12.1

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