Unable to get stmmac driver of Altera Cyclone V to support MTU9000

Unable to get stmmac driver of Altera Cyclone V to support MTU9000

[Teoh Choon Zone]

According to the technical reference manual, Cyclone V does support jumbo
frame up to 9.6KB, which I read as it will support MTU up to 9000. But I
couldn't get it to work properly with MTU9000.

I define working as in I can ping with a packet size of 9000 bytes, e.g
"ping <host> -s 9000", the ping process just won't start when I set the MTU
anything larger then 8144. FYI, tx is running in store-and-forward mode and
rx is running in threshold mode.

Anyone know how I can tweak the stmmac driver to support MTU9000?
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Unable to get stmmac driver of Altera Cyclone V to support MTU9000

[Valdis.Kletnieks at vt.edu]

On Tue, 22 Sep 2015 23:49:18 +0800, Teoh Choon Zone said:

> I define working as in I can ping with a packet size of 9000 bytes, e.g
> "ping <host> -s 9000", the ping process just won't start when I set the MTU
> anything larger then 8144.

1)  When you set the MTU, does it show up as set if you do 'ifconfig eth2'
or whatever it is?>

2) In what way *exactly* does the ping "just won't start"?  Any error
messages?  If you run 'strace ping' where does it look like it all goes
astray?
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Unable to get stmmac driver of Altera Cyclone V to support MTU9000

[Teoh Choon Zone]

> When you set the MTU, does it show up as set if you do 'ifconfig eth2'
> or whatever it is?
I can see it being set successfully.


> In what way *exactly* does the ping "just won't start"?  Any error
> messages?  If you run 'strace ping' where does it look like it all goes
> astray?
When I "ping 192.168.128.99 -s 9000", what I can only see is "PING
192.168.128.99 (192.168.128.99) 9000(9028) bytes of data.", nothing else.
But when I "ping 192.168.128.99 -s 8144", I can get "8152 bytes from
192.168.128.99: icmp_req=2 ttl=64 time=1.05 ms"
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Unable to get stmmac driver of Altera Cyclone V to support MTU9000

[Pranay Srivastava]

Hi Teoh,

On Mon, Sep 28, 2015 at 7:17 AM, Teoh Choon Zone
<choon-zone.teoh@vie.com.my> wrote:
>> When you set the MTU, does it show up as set if you do 'ifconfig eth2'
>> or whatever it is?
> I can see it being set successfully.
>
>
>> In what way *exactly* does the ping "just won't start"?  Any error
>> messages?  If you run 'strace ping' where does it look like it all goes
>> astray?
> When I "ping 192.168.128.99 -s 9000", what I can only see is "PING
> 192.168.128.99 (192.168.128.99) 9000(9028) bytes of data.", nothing else.

Have you tried the above with 8972 to instead of 9000.

> But when I "ping 192.168.128.99 -s 8144", I can get "8152 bytes from
> 192.168.128.99: icmp_req=2 ttl=64 time=1.05 ms"
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>



-- 
        ---P.K.S

Unable to get stmmac driver of Altera Cyclone V to support MTU9000

[Teoh Choon Zone]

> Have you tried the above with 8972 to instead of 9000.
Yes, but nothing above 8144 works.
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Unable to get stmmac driver of Altera Cyclone V to support MTU9000

[Valdis.Kletnieks at vt.edu]

On Mon, 28 Sep 2015 10:14:47 +0800, Teoh Choon Zone said:

> > Have you tried the above with 8972 to instead of 9000.
> Yes, but nothing above 8144 works.

It's possible it's a defective design, and is crippled so it can manage
8144 but not the 9000 most chipsets can do.  The fact that 8144 works
is proof the chipset *does* have a concept of jumbograms - but there's
been a *lot* of misdesigned chips that have this sort of issue....

Your choices may be limited to running the subnet with an MTU of 8144, or
replacing the defective card.  Have you found anything online claiming that
the card *can* specifically support MTU=9000?, or reached out to the
company?
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Unable to get stmmac driver of Altera Cyclone V to support MTU9000

[Teoh Choon Zone]

On Mon, Sep 28, 2015 at 11:39 AM, <Valdis.Kletnieks@vt.edu> wrote:

> It's possible it's a defective design, and is crippled so it can manage
> 8144 but not the 9000 most chipsets can do.  The fact that 8144 works
> is proof the chipset *does* have a concept of jumbograms - but there's
> been a *lot* of misdesigned chips that have this sort of issue....
>
> Your choices may be limited to running the subnet with an MTU of 8144, or
> replacing the defective card.  Have you found anything online claiming that
> the card *can* specifically support MTU=9000?, or reached out to the
> company?
>

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.

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.

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:

In functions stmmac_jumbo_frm,
desc->des2 = dma_map_single(priv->device, skb->data,
   bmax, DMA_TO_DEVICE); // where bmax is 8192
desc->des3 = desc->des2 + BUF_SIZE_4KiB;


In functions stmmac_refill_desc3 and stmmac_init_desc3
p->des3 = p->des2 + BUF_SIZE_8KiB;

Although the maximum FIFO size are 8kB for both of them (verified from
descs.h), why is the offset are different?
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