<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Mon, Sep 28, 2015 at 11:39 AM, <span dir="ltr"><<a href="mailto:Valdis.Kletnieks@vt.edu" target="_blank">Valdis.Kletnieks@vt.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">It's possible it's a defective design, and is crippled so it can manage<br>
8144 but not the 9000 most chipsets can do. The fact that 8144 works<br>
is proof the chipset *does* have a concept of jumbograms - but there's<br>
been a *lot* of misdesigned chips that have this sort of issue....<br>
<br>
Your choices may be limited to running the subnet with an MTU of 8144, or<br>
replacing the defective card. Have you found anything online claiming that<br>
the card *can* specifically support MTU=9000?, or reached out to the<br>
company?<br>
</blockquote></div><br></div><div class="gmail_extra">Actually initially I can only ping up to MTU 4042, and I have clarified with Altera, they also said that is the maximum MTU supported. </div><div class="gmail_extra"><br></div><div class="gmail_extra">But after that I learned from the technical reference manual and play around with the stmmac driver, if I run Tx in store-and-forward mode and Rx in threshold mode, I can ping up to MTU 8144. And according to the TRM, the GMAC indeed can support up to MTU 9.6KB. That's why I'm thinking maybe is the ethernet driver has some parts need to be configured properly to suit my particular GMAC.</div><div class="gmail_extra"><br></div><div class="gmail_extra">In particular, I've a hunch that this is related to the FIFO size and descriptor offset. The GMAC that I'm using has Tx and Rx FIFO size of 4kB each and supports up to 8kB descriptor. The confusing part are the following lines in ring_mode.c:</div><div class="gmail_extra"><br></div><div class="gmail_extra">In functions stmmac_jumbo_frm,</div><div class="gmail_extra"><div class="gmail_extra">desc->des2 = dma_map_single(priv->device, skb->data,</div><div class="gmail_extra"><span class="" style="white-space:pre"> </span> bmax, DMA_TO_DEVICE); // where bmax is 8192</div><div class="gmail_extra">desc->des3 = desc->des2 + BUF_SIZE_4KiB;<br></div><div class="gmail_extra"><br></div><div class="gmail_extra"><br></div><div class="gmail_extra">In functions stmmac_refill_desc3 and stmmac_init_desc3</div><div class="gmail_extra">p->des3 = p->des2 + BUF_SIZE_8KiB;<br></div><div class="gmail_extra"><br></div><div class="gmail_extra">Although the maximum FIFO size are 8kB for both of them (verified from descs.h), why is the offset are different?</div><div class="gmail_extra"><br></div></div></div>