Re: [Qemu-devel] [PATCH 05/17] imx_fec: Use ENET_FTRL to determine truncation length

[Peter Maydell]

On 30 September 2017 at 01:17, Philippe Mathieu-Daudé <address@hidden> wrote:
> Hi Andrey,
>
> On 09/18/2017 04:50 PM, Andrey Smirnov 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.
>>
>> 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 | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/net/imx_fec.c b/hw/net/imx_fec.c
>> index 767402909d..989c11be5f 100644
>> --- a/hw/net/imx_fec.c
>> +++ b/hw/net/imx_fec.c
>> @@ -1050,8 +1050,8 @@ static ssize_t imx_enet_receive(NetClientState *nc,
>> const uint8_t *buf,
>>       size += 4;
>>         /* 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;
>>       }
>
>
> for this to be ok you need to update imx_enet_write(), such:
>
>      case ENET_FTRL:
> -        s->regs[index] = value & 0x00003fff;
> +        value &= 0x00003fff;
> +        if (value > ENET_MAX_FRAME_SIZE) {
> +            warn_report("%s: guest requested bigger "
> +                        "frame size than QEMU supports "
> +                        "(%u > %u)", value,
> +                        ENET_MAX_FRAME_SIZE);
> +            value = ENET_MAX_FRAME_SIZE;
> +        }
> +        s->regs[index] = value;
>          break;

Yes, and also an incoming-migration post_load callback that
fails migration if the value is too large.

It might be simpler to truncate to the smaller of the ENET_FTRL
register value and ENET_MAX_FRAME_SIZE.

(PS: what is the hardware behaviour if ENET_FTRL is set to
a larger value than ENET_MAX_FRAME_SIZE ?)

thanks
-- PMM