Ernst J. Oud a écrit :
> L.S.
>
> Mmm.... I might be onto something about this weird MTU problem with Zydas 
> 1211b based devices on my embedded box.
>
> This box has an RDC i486 SOC processor.
>
> Within the vendor driver of the Zydas 1211b there is an extra compiler flag 
> called "ZDCONF_R8610_FRAG_FIX" (r8610 is an RDC i486 compatible SOC), it is 
> only tested in the vendor module zd1205c as follows:
>
> (small snippet of code, arrow is mine)
>
>    //copy packet for IP header is located on 4-bytes alignment
> #if ZDCONF_R8610_FRAG_FIX == 1 
> <<<<<<<<<<<<<<<<<<-------------------
>     if (1)
> #else
>     if (length < RX_COPY_BREAK)
> #endif
>     {
>         dev_kfree_skb_any(skb);
>         skb = dev_alloc_skb(length+2);
>
>         if (skb){
>             skb->dev = g_dev;
>             skb_reserve(skb, 2);
>             skb_copy_from_linear_data(skb,pData,length);
>             skb_put(skb, length);
>         }
>     }
>     else{
>     #ifdef NET_SKBUFF_DATA_USES_OFFSET
>         skb->tail = 0;
>         skb->data = pData;
>     #else
>         skb->tail = skb->data = pData;
>     #endif
>         skb_put(skb, length);
>     }
>
> i.e. if the flag is set in the receiver code a number of statements is 
> always executed on an R8610...
>
> I reckon this certainly might be the reason of my MTU > 500 problem... seems 
> plausible.
>
> This weird patch is of course not present in the community driver.
>
> Any comments?
>
> TIA
>
> Regards,
>
> Ernst
>   
Hello Ernst,

Regarding the source code you mentioned, I cannot find the R8610 thing. 
Which version/revision do you look at? Moreover, the RX_COPY_BREAK is 0 
in the source code I've looked at and this code is only used for RX (not 
TX), so it's unlikely to be the root cause of your problem.

My guess is that it could be a USB 1.1 versus 2.0 problem. Can you 
provide the output of lsusb -t on your SoC when the stick is plugged in?

Regards,
Benoit


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