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Re: [PATCH] hw/net: npcm7xx_emc fix missing queue_flush


From: Patrick Venture
Subject: Re: [PATCH] hw/net: npcm7xx_emc fix missing queue_flush
Date: Fri, 3 Dec 2021 14:10:41 -0800



On Fri, Dec 3, 2021 at 1:54 PM Patrick Venture <venture@google.com> wrote:


On Fri, Dec 3, 2021 at 1:42 PM Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
On 12/3/21 22:27, Patrick Venture wrote:
> The rx_active boolean change to true should always trigger a try_read
> call that flushes the queue.
>
> Signed-off-by: Patrick Venture <venture@google.com>
> ---
>  hw/net/npcm7xx_emc.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/hw/net/npcm7xx_emc.c b/hw/net/npcm7xx_emc.c
> index 7c892f820f..97522e6388 100644
> --- a/hw/net/npcm7xx_emc.c
> +++ b/hw/net/npcm7xx_emc.c
> @@ -581,13 +581,6 @@ static ssize_t emc_receive(NetClientState *nc, const uint8_t *buf, size_t len1)
>      return len;
>  }

> -static void emc_try_receive_next_packet(NPCM7xxEMCState *emc)
> -{
> -    if (emc_can_receive(qemu_get_queue(emc->nic))) {
> -        qemu_flush_queued_packets(qemu_get_queue(emc->nic));
> -    }
> -}

What about modifying as emc_flush_rx() or emc_receive_and_flush()
helper instead?

 static void emc_flush_rx(NPCM7xxEMCState *emc)
 {
     emc->rx_active = true;
     qemu_flush_queued_packets(qemu_get_queue(emc->nic));
 }

I'm ok with that idea, although I'm less fond that it _hides_ the rx_active=true.  There is an emc_halt_rx that hides rx_active=false, so one could argue it's not an issue. Looking at ftgmac100, it mostly just calls the qemu_flush_queued_packets inline where it needs it.  So given the prior art, I'm more inclined to leave this as a two-line pair, versus collapsing it into a method.  Mostly because I don't anticipate this call being made from any other places, so it's not a "growing" device.  The method originally was emc_try_receive_next_packet, which didn't do anything more than a no-op check and the queue_flush.  The new method would move the rx_active setting from the call that deliberately controls it (the register change) into a subordinate method...

Beyond all that, I think it's fine either way.  Feel free to push back and I'll make the change.

I figured why not :) And just made the change and sent out a v2. 

>  static uint64_t npcm7xx_emc_read(void *opaque, hwaddr offset, unsigned size)
>  {
>      NPCM7xxEMCState *emc = opaque;
> @@ -704,6 +697,7 @@ static void npcm7xx_emc_write(void *opaque, hwaddr offset,
>          }
>          if (value & REG_MCMDR_RXON) {
>              emc->rx_active = true;
> +            qemu_flush_queued_packets(qemu_get_queue(emc->nic));
>          } else {
>              emc_halt_rx(emc, 0);
>          }
> @@ -740,7 +734,7 @@ static void npcm7xx_emc_write(void *opaque, hwaddr offset,
>      case REG_RSDR:
>          if (emc->regs[REG_MCMDR] & REG_MCMDR_RXON) {
>              emc->rx_active = true;
> -            emc_try_receive_next_packet(emc);
> +            qemu_flush_queued_packets(qemu_get_queue(emc->nic));
>          }
>          break;
>      case REG_MIIDA:
>


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