[U-Boot] [PATCH 0/2] Add fix for Pine64 gigabit throughput issues

[Kyle Evans]

On Thu, Feb 15, 2018 at 3:32 PM, André Przywara <andre.przywara at arm.com> wrote:
> Hi,
>
> thanks for picking this up!
>
> (CC:ing Icenowy, who was engaged in a Linux fix for this issue last year
> [2][3]. It's Chinese New Year though, so not sure how quickly she will
> answer).
>
> On 14/02/18 23:02, kevans at FreeBSD.org wrote:
>> The Pine64 has a known issue on gigabit links (see [1]); some boards suffer
>> significant packet loss on Gigabit links.
>
> Do you have a faulty board at hand? What is the actual effect in U-Boot?
> IIRC the bug "just" causes a slower connection in Gigabit mode, I am not
> sure we care so much in U-Boot? Or is it actually packages dropped,
> which is much more annoying without TCP covering up for this?

I do. =) My board in particular sees 60-70% packet loss without this,
making netboot incredibly unreliable.

>
>> This patch sets the magical bits
>> in CONFREG on the RTL8211E PHY to turn off the internal delay and do some other
>> undocumented stuff.
>
> So if I remember the discussion correctly, this workaround affects the
> performance of the "good" boards. Have you checked this?
> There was a discussion last year [2][3] about how to fix this in Linux,
> which definitely involved some DT property (ideally in the PHY node).
> This would allow people to turn this on and off depending on their
> particular board.
> I am not sure this discussion lead anywhere, though, it might be a good
> idea to warm this up again.
>

Unfortunately, I do not have a good board to test with, so I've no
idea what it ends up doing to performance. for them.

I think rgmii-txid is actually not right for this. As an aside, I've
pulled this value from [1]. The value they ended up going with (as
seen in this patch and in [1]) turns off both TXID and RXID (IIRC,
from the realtek documentation for this PHY), leaving us with just
plain ol' "rgmii" with no internal delay at all. [1] also applies it
unconditionally for pine64.

[1] https://github.com/longsleep/linux-pine64/commit/ffe3ca5be7682bbeb0fdadede29acd4a3c888015