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

[Stefan Roese]

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.

> Or any reason why the packet is not correctly transferred? Do you see
> errors on the line or the packet vanishes completely ?
> What kind of packet is this first one ? Does it depend on the packet type ?

I did not check too closely, as this issue was so similar to the
ones I've seen before in U-Boot (see above). It happens upon
"ping" and "tftp" - that's what I did test with.
  
> Sorry for maybe asking too many questions.

No need to be sorry. If this can be solved in another perhaps
cleaner way, I'll gladly use another solution.
  
> I have added Nicolas and Claudiu who have more experience with macb on
> at91 boards

Sure, let's see what others have to say on this. Did someone else
notice these timeouts resulting in quite big delays?

Thanks,
Stefan