dmaengine: ste_dma40: don't allow high priority dest event lines

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@stericsson.com>
Reviewed-by: Shreshtha Kumar Sahu <shreshthakumar.sahu@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>

diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c
index 760576b85641215db5a3125cf4222c1a29fa6f73..9f8964a0a2874a54495f6d9fb726b5d97f5639ac 100644 (file)
--- a/drivers/dma/ste_dma40.c
+++ b/drivers/dma/ste_dma40.c
@@ -2180,11 +2180,24 @@ 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)