Re: [Qemu-arm] [PATCH 02/17] imx_fec: Do not calculate FEC

[Peter Maydell]

On 18 September 2017 at 20:50, Andrey Smirnov <address@hidden> wrote:
> Save some computation time and avoid calculating CRC's frame
>
> Cc: Peter Maydell <address@hidden>
> Cc: Jason Wang <address@hidden>
> Cc: address@hidden
> Cc: address@hidden
> Cc: address@hidden
> Signed-off-by: Andrey Smirnov <address@hidden>
> ---
>  hw/net/imx_fec.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/hw/net/imx_fec.c b/hw/net/imx_fec.c
> index 88b4b049d7..75822344fc 100644
> --- a/hw/net/imx_fec.c
> +++ b/hw/net/imx_fec.c
> @@ -1032,9 +1032,7 @@ static ssize_t imx_enet_receive(NetClientState *nc, 
> const uint8_t *buf,
>      IMXENETBufDesc bd;
>      uint32_t flags = 0;
>      uint32_t addr;
> -    uint32_t crc;
>      uint32_t buf_addr;
> -    uint8_t *crc_ptr;
>      unsigned int buf_len;
>      size_t size = len;
>
> @@ -1048,8 +1046,6 @@ static ssize_t imx_enet_receive(NetClientState *nc, 
> const uint8_t *buf,
>
>      /* 4 bytes for the CRC.  */
>      size += 4;
> -    crc = cpu_to_be32(crc32(~0, buf, size));
> -    crc_ptr = (uint8_t *) &crc;
>
>      /* Huge frames are truncted.  */
>      if (size > ENET_MAX_FRAME_SIZE) {
> @@ -1090,9 +1086,10 @@ static ssize_t imx_enet_receive(NetClientState *nc, 
> const uint8_t *buf,
>          dma_memory_write(&address_space_memory, buf_addr, buf, buf_len);
>          buf += buf_len;
>          if (size < 4) {
> +            const uint8_t zeros[4] = { 0 };
> +
>              dma_memory_write(&address_space_memory, buf_addr + buf_len,
> -                             crc_ptr, 4 - size);
> -            crc_ptr += 4 - size;
> +                             zeros, 4 - size);
>          }
>          bd.flags &= ~ENET_BD_E;
>          if (size == 0) {

This looks a bit odd. Doesn't the hardware calculate the CRC here?

thanks
-- PMM