Messages in this thread | | | From | Xiaoliang Yang <> | Subject | RE: [EXT] Re: [net-next] net: dsa: felix: disable always guard band bit for TAS config | Date | Wed, 9 Jun 2021 08:06:03 +0000 |
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On 2021-06-07 19:26, Michael Walle wrote: > > Hi Vladimir, Hi Xiaoliang, > > Am 2021-05-07 14:19, schrieb Vladimir Oltean: > > Devices like Felix need the per-queue max SDU from the user - if that > > isn's specified in the netlink message they'll have to default to the > > interface's MTU. > > Btw. just to let you and Xiaoliang know: > > It appears that PORT_MAX_SDU isn't working as expected. It is used as a > fallback if QMAXSDU_CFG_n isn't set for the guard band calculation. But it > appears to be _not_ used for discarding any frames. E.g. if you set > PORT_MAX_SDU to 500 the port will still happily send frames larger than 500 > bytes. (Unless of course you hit the guard band of 500 bytes). OTOH > QMAXSDU_CFG_n works as expected, it will discard oversized frames - and > presumly will set the guard band accordingly, I haven't tested this explicitly. > > Thus, I wonder what sense PORT_MAX_SDU makes at all. If you set the guard > band to a smaller value than the MTU, you'll also need to make sure, there will > be no larger frames scheduled on that port. > > In any case, the workaround is to set QMAXSDU_CFG_n (for all > n=0..7) to the desired max_sdu value instead of using PORT_MAX_SDU. > > It might also make sense to check with the IP supplier. > > In the case anyone wants to implement that for (upstream) linux ;) > > -michael
Yes, PORT_MAX_SDU is only used for guard band calculation. DEV_GMII: MAC_MAXLEN_CFG limited the frame length accepted by the MAC. I am worried that QMAXSDU is not a universal setting, it may just be set on Felix, so there is no suitable place to add this configuration.
Thanks, xiaoliang
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