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

[Eugen.Hristev at microchip.com]

On 29.03.2019 17:24, Stefan Roese wrote:

> 
> 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.

Hi Joe,

If you agree with this change I will take it through my tree. Or any 
feedback appreciated from you or someone familiar with the macb / 
network devices.

Thanks !
Eugen

> 
> Thanks,
> Stefan