hw/dma: sifive_pdma: don't set Control.error if 0 bytes to transfer

Real PDMA doesn't set Control.error if there are 0 bytes to be
transferred. The DMA transfer is still success.

The following result is PDMA tested in U-Boot on Unmatched 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 0x0                      <= NextBytes = 0
=> 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 00000000 00000000    .......U........
03000010: 84000000 00000000 84001000 00000000    ................
=> mw.l 0x3000000 0x3                      <= Set channel 0 run and claim bits
=> md.l 0x3000000 8                        <= Dump PDMA status
03000000: 40000001 55000000 00000000 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: Frank Chang <frank.chang@sifive.com>
Tested-by: Max Hsu <max.hsu@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Message-id: 20210912130553.179501-5-frank.chang@sifive.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

hw/dma/sifive_pdma.c

@@ -80,7 +80,7 @@ static void sifive_pdma_run(SiFivePDMAState *s, int ch)
 
     /* do nothing if bytes to transfer is zero */
     if (!bytes) {
-        goto error;
+        goto done;
     }
 
     /*
@@ -135,18 +135,18 @@ static void sifive_pdma_run(SiFivePDMAState *s, int ch)
         s->chan[ch].exec_bytes -= remainder;
     }
 
-    /* indicate a DMA transfer is done */
-    s->chan[ch].state = DMA_CHAN_STATE_DONE;
-    s->chan[ch].control &= ~CONTROL_RUN;
-    s->chan[ch].control |= CONTROL_DONE;
-
     /* reload exec_ registers if repeat is required */
     if (s->chan[ch].next_config & CONFIG_REPEAT) {
         s->chan[ch].exec_bytes = bytes;
         s->chan[ch].exec_dst = dst;
         s->chan[ch].exec_src = src;
     }
 
+done:
+    /* indicate a DMA transfer is done */
+    s->chan[ch].state = DMA_CHAN_STATE_DONE;
+    s->chan[ch].control &= ~CONTROL_RUN;
+    s->chan[ch].control |= CONTROL_DONE;
     return;
 
 error: