Re: [Qemu-devel] [PATCH v3 04/30] imx_fec: Use ENET_FTRL to determine truncation length

[Peter Maydell]

On 6 November 2017 at 15:47, Andrey Smirnov <address@hidden> wrote:
> Frame truncation length, TRUNC_FL, is determined by the contents of
> ENET_FTRL register, so convert the code to use it instead of a
> hardcoded constant.
>
> To avoid the case where TRUNC_FL is greater that ENET_MAX_FRAME_SIZE,
> increase the value of the latter to its theoretical maximum of 16K.
>
> Cc: Peter Maydell <address@hidden>
> Cc: Jason Wang <address@hidden>
> Cc: Philippe Mathieu-Daudé <address@hidden>
> Cc: address@hidden
> Cc: address@hidden
> Cc: address@hidden
> Signed-off-by: Andrey Smirnov <address@hidden>
> ---
>  hw/net/imx_fec.c         | 4 ++--
>  include/hw/net/imx_fec.h | 3 ++-
>  2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/hw/net/imx_fec.c b/hw/net/imx_fec.c
> index eb034ffd0c..dda0816fb3 100644
> --- a/hw/net/imx_fec.c
> +++ b/hw/net/imx_fec.c
> @@ -1052,8 +1052,8 @@ static ssize_t imx_enet_receive(NetClientState *nc, 
> const uint8_t *buf,
>      crc_ptr = (uint8_t *) &crc;
>
>      /* Huge frames are truncted.  */
> -    if (size > ENET_MAX_FRAME_SIZE) {
> -        size = ENET_MAX_FRAME_SIZE;
> +    if (size > s->regs[ENET_FTRL]) {
> +        size = s->regs[ENET_FTRL];
>          flags |= ENET_BD_TR | ENET_BD_LG;
>      }
>
> diff --git a/include/hw/net/imx_fec.h b/include/hw/net/imx_fec.h
> index 4bc8f03ec2..0fcc4f0c71 100644
> --- a/include/hw/net/imx_fec.h
> +++ b/include/hw/net/imx_fec.h
> @@ -86,7 +86,6 @@
>  #define ENET_TCCR3             393
>  #define ENET_MAX               400
>
> -#define ENET_MAX_FRAME_SIZE    2032
>
>  /* EIR and EIMR */
>  #define ENET_INT_HB            (1 << 31)
> @@ -155,6 +154,8 @@
>  #define ENET_RCR_NLC           (1 << 30)
>  #define ENET_RCR_GRS           (1 << 31)
>
> +#define ENET_MAX_FRAME_SIZE    (1 << ENET_RCR_MAX_FL_LENGTH)

This means we now have functions with 16K local array
variables on the stack, which seems like a bad idea.

thanks
-- PMM