[U-Boot] [PATCH] net: macb: Add small delay after link establishment

[Stefan Roese]

On 29.03.19 15:59, Eugen.Hristev at microchip.com wrote:
> 
> 
> On 29.03.2019 16:52, Stefan Roese wrote:
> 
>> Hi Eugen,
>>
>> On 29.03.19 15:40, Eugen.Hristev at microchip.com wrote:
>>>> I've noticed that the first ethernet packet after PHY link establishment
>>>> is not tranferred correctly most of the time on my AT91SAM9G25 board.
>>>> Here I usually see a timeout of a few seconds, which is quite
>>>> annoying.
>>>>
>>>> Adding a small delay (10ms in this case) after the link establishment
>>>> helps to solve this problem. With this patch applied, this timeout
>>>> on the first packet is not seen any more.
>>>
>>> Hi Stefan,
>>>
>>> I find this a bit odd... maybe someone with a different board having
>>> this Ethernet controller can confirm or infirm this ?
>>
>> I've seen such issues of timeouts with the first ethernet packet
>> after link negotiation on other platforms / controllers a few
>> times before in U-Boot. Using a short delay after link-up always
>> did help here.
>>
>> I'm not saying that this is the perfect solution, but its one that
>> works and removes these timeouts, which really annoy me.
>>
>>> Linux driver for macb has a similar issue ?
>>
>> Not that I am aware of. There might be some delay in the link
>> establishment hidden as well. I did not check yet.
>>
>>> Adding a delay just for the sake of it might hide another issue that we
>>> are missing at this point: why exactly transfer fails right away... it
>>> is likely that we want to send packets but link in fact is not ready ?
>>
>> Yes, something like this.
> 
> I see there is a small udelay below your code, you add a delay 100 times
> bigger... maybe that small delay is related ?

The udelay(100) below is for the timeout handling of the link autoneg
loop. This should be probably moved to some loop using get_timer() so
that this udelay can be removed completely.

Coming back to your question, if these delays are related. No, they
are not. The one that I insert is explicitly added *after* the link
was established. I could experiment if a smaller value also works, but
I found that 100ms was working in all my test cases. Possibly 10ms
or even 1ms also works. Not sure.

Thanks,
Stefan