Re: [PATCH v2 2/2] hw/dma: sifive_pdma: Don't run DMA when channel is disclaimed

[Alistair Francis]

On Mon, Sep 27, 2021 at 5:22 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> 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>

Acked-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

>
> ---
>
> (no changes since v1)
>
>  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
>
>