[PATCH 2/2] hw/dma: sifive_pdma: Don't run DMA when channel is disclaimed

[Bin Meng]

If Control.run bit is set while not preserving the Control.claim
bit, the DMA transfer shall not be started.

The following result is PDMA tested in U-Boot on Unleashed board:

=> mw.l 0x3000000 0x0                      <= Disclaim channel 0
=> mw.l 0x3000000 0x1                      <= Claim channel 0
=> mw.l 0x3000004 0x55000000               <= wsize = rsize = 5 (2^5 = 32 bytes)
=> mw.q 0x3000008 0x2                      <= NextBytes = 2
=> mw.q 0x3000010 0x84000000               <= NextDestination = 0x84000000
=> mw.q 0x3000018 0x84001000               <= NextSource = 0x84001000
=> mw.l 0x84000000 0x87654321              <= Fill test data to dst
=> mw.l 0x84001000 0x12345678              <= Fill test data to src
=> md.l 0x84000000 1; md.l 0x84001000 1    <= Dump src/dst memory contents
84000000: 87654321                               !Ce.
84001000: 12345678                               xV4.
=> md.l 0x3000000 8                        <= Dump PDMA status
03000000: 00000001 55000000 00000002 00000000    .......U........
03000010: 84000000 00000000 84001000 00000000    ................
=> mw.l 0x3000000 0x2                      <= Set channel 0 run bit only
=> md.l 0x3000000 8                        <= Dump PDMA status
03000000: 00000000 55000000 00000002 00000000    .......U........
03000010: 84000000 00000000 84001000 00000000    ................
=> md.l 0x84000000 1; md.l 0x84001000 1    <= Dump src/dst memory contents
84000000: 87654321                               !Ce.
84001000: 12345678                               xV4.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
---

 hw/dma/sifive_pdma.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/hw/dma/sifive_pdma.c b/hw/dma/sifive_pdma.c
index b8ec7621f3..85fe34f5f3 100644
--- a/hw/dma/sifive_pdma.c
+++ b/hw/dma/sifive_pdma.c
@@ -232,7 +232,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
 {
     SiFivePDMAState *s = opaque;
     int ch = SIFIVE_PDMA_CHAN_NO(offset);
-    bool claimed;
+    bool claimed, run;
 
     if (ch >= SIFIVE_PDMA_CHANS) {
         qemu_log_mask(LOG_GUEST_ERROR, "%s: Invalid channel no %d\n",
@@ -244,6 +244,7 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
     switch (offset) {
     case DMA_CONTROL:
         claimed = !!(s->chan[ch].control & CONTROL_CLAIM);
+        run = !!(s->chan[ch].control & CONTROL_RUN);
 
         if (!claimed && (value & CONTROL_CLAIM)) {
             /* reset Next* registers */
@@ -254,13 +255,19 @@ static void sifive_pdma_write(void *opaque, hwaddr offset,
             s->chan[ch].next_src = 0;
         }
 
+        /* claim bit can only be cleared when run is low */
+        if (run && !(value & CONTROL_CLAIM)) {
+            value |= CONTROL_CLAIM;
+        }
+
         s->chan[ch].control = value;
 
         /*
          * If channel was not claimed before run bit is set,
+         * or if the channel is disclaimed when run was low,
          * DMA won't run.
          */
-        if (!claimed) {
+        if (!claimed || (!run && !(value & CONTROL_CLAIM))) {
             s->chan[ch].control &= ~CONTROL_RUN;
             return;
         }
-- 
2.25.1