Subject: Re: [PATCH 1/1 net-next] net: fec: enable pause frame to improve rx prefomance for 1G network

From: Eric Nelson <[email-masked]>
Date: Tue, 08 Jan 2013 09:13:41 -0700

On 01/08/2013 02:55 AM, Dirk Behme wrote:
> On 08.01.2013 09:43, Frank Li wrote:
>> The limition of imx6 internal bus cause fec can't achieve 1G perfomance.
>> There will be many packages lost because FIFO over run.
>>
>> This patch enable pause frame flow control.
>
> Many thanks for this patch!
>
> Do we want/need anything similar for U-Boot, too?
>
> Some people want to boot the system from U-Boot attached to 1G network
> and have issues there, too.
>

It's hard to see how the typical use (dhcp+tftp) would be affected
because of the small packet sizes and half-duplex operation.

That said, the statistics registers make it pretty easy to see when
there are overflows as described here:
	http://boundarydevices.com/i-mx6-ethernet/

We should be able to just poke the ENET_MIBC register and watch
to see if the IEEE_R_MACERR register shows that overruns are
occurring using the U-Boot md and mw commands.

In a quick test, it appears that this doesn't work though.
This line of code in fec_halt from fec_mxc.c seems to clear the
statistics.

	writel(readl(&fec->eth->ecntrl) & ~FEC_ECNTRL_ETHER_EN,
			&fec->eth->ecntrl);

If you comment that out, you can see all of the statistics registers
as shown below:

U-Boot > mw.l 0x02188064 0    #ENET_MIBC
U-Boot > dhcp 10800000 192.168.0.55:uImage-bluemeany
BOOTP broadcast 1
DHCP client bound to address 192.168.0.91
Using FEC device
TFTP from server 192.168.0.55; our IP address is 192.168.0.91
Filename 'uImage-bluemeany'.
Load address: 0x10800000
Loading: ...
done
Bytes transferred = 3760504 (396178 hex)
U-Boot > md.l 0x02188200 0x39
02188200: 00000000 00001cb6 00000003 00000000    ................
02188210: 00000000 00000000 00000000 00000000    ................
02188220: 00000000 00000000 00001cb2 00000002    ................
02188230: 00000000 00000002 00000000 00000000    ................
02188240: 00000000 00072fd4 00000000 00001cb6    ...../..........
02188250: 00000000 00000000 00000000 00000000    ................
02188260: 00000000 00000000 00000000 00000000    ................
02188270: 00000000 00072fd4 00000000 00000000    ...../..........
02188280: 00000000 00001dca 0000002a 000000e6    ........*.......
02188290: 00000000 00000000 00000000 00000000    ................
021882a0: 00000000 00000000 00000037 00000057    ........7...W...
021882b0: 0000004e 00000023 00001ccb 00000000    N...#...........
021882c0: 00000000 003fd011 00000000 00001dcc    ......?.........
021882d0: 00000000 00000000 00000000 00000000    ................
021882e0: 003fd011    ..?.
U-Boot >

Register 0x021882d8 is the MACERR (fifo overlow) counter.

Regards,

Eric