[U-Boot] [linux-sunxi] Re: [PATCH] sunxi: Fix gmac not working reliable on the Bananapi

[jonsmirl at gmail.com]

On Mon, Sep 29, 2014 at 2:16 PM, Karsten Merker <merker at debian.org> wrote:
> On Mon, Sep 29, 2014 at 09:13:37AM +0300, Siarhei Siamashka wrote:
>
>> On Sun, 28 Sep 2014 20:13:21 +0200
>> Hans de Goede <hdegoede at redhat.com> wrote:
>>
>> > In order for the gmac nic to work reliable on the Bananapi, we need to poke
>> > these 2 undocumented bits in the gmac clk register. Since these are
>> > undocumented, this commit only sets these bits on the Bananapi for now.
>> >
>> > I'll contact Allwinner to try and get these bits documented, once they
>> > are documented we can hopefully replace this hack with a better patch.
>>
>> Could you please provide a bit more details in the commit message?
>> What are the symptoms of the problem?
>
> Without the patch, u-boot on the BananaPi shows massive packet loss
> on every network activity.  The packet loss is so extreme that it is
> actually impossible to boot a kernel by tftp because u-boot gives up.
> The mainline kernel has (once booted) shown similar problems on the
> BananaPi.
>
>> How did you come to the idea to poke these bits?
>
> The linux 3.4 kernel from https://github.com/LeMaker/linux-bananapi
> (which is a patched linux-sunxi.org 3.4 kernel) does not show this
> problem, so we started looking into what is different there, and the
> relevant change that was found was setting these particular
> undocumented bits.

File at issue here asking for the documentation
https://github.com/allwinner-zh/documents

>
>> Does the GMAC driver in the linux kernel need a similar
>> fix/workaround?
>
> Not as far as I can see - once u-boot has set these two bits during
> system initialization, the mainline kernel works fine without
> any changes.
>
>> Also as mentioned in another e-mail
>>     http://lists.denx.de/pipermail/u-boot/2014-September/190096.html
>> u-boot configures the "912MHz @1.4V" CPU clock frequency/voltage
>> setup for sun7i hardware. And according to the information from Tony
>> Zhang, this is supposed to be unreliable for the Banana Pi. So what
>> happens to this GMAC bug if you just increase the dcdc2 voltage in
>> u-boot (or reduce the CPU clock frequency)?
>
> I can test that if you could tell me what would have to be changed
> in u-boot to do that.
>
> Regards,
> Karsten
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-- 
Jon Smirl
jonsmirl at gmail.com