RE: [PATCH v2 00/11] ARM: dts: zynq: Prepare Parallella

[Soren Brinkmann]

Sorry, for top-posting, but I currently just have Outlook webmail.
The cause for this issue is relatively easily identified. The ethernet drivers sets the Ethernet clock according to the negotioated link speed. For this adjustment a 6-bit divider in the clock path is used. In this case, it seems, the input to the 6-bit divider doesn't allow generating the full range of required frequencies for all supported link speeds.

I guess this could be solved in multiple ways.
1. Disable 1G mode/auto negotiation, the other modes are probably fine (yeah, not a solution, but might give you a working ethernet link)
2. Ensure the divider input allows to generate all required frequencies. This essentially means to go back into Xilinx tools and play around with the clock/PLL setup and re-generating a bootloader that sets things up with the updated values.
3. Support to run-time-adust the PLLs in Zynq. This is definitely the most complex one. I never seriously pursued this, since it seemed close to impossible to change the PLLs at run-time without crashing pretty much every downstream user except for the one that requested the frequency change. And even if every driver would be able to handle such a change, I could imagine that frequency constraints from  all the drivers together would still prevent any change.

        Thanks,
        Sören

________________________________________
From: devicetree-owner@xxxxxxxxxxxxxxx [devicetree-owner@xxxxxxxxxxxxxxx] on behalf of Olof Johansson [olof@xxxxxxxxx]
Sent: Friday, October 17, 2014 9:28 PM
To: Andreas Färber
Cc: Michal Simek; Andreas Olofsson; Matteo Vit; Sean Rickerd; devicetree@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Punnaiah Choudary Kalluri; Lars-Peter Clausen
Subject: Re: [PATCH v2 00/11] ARM: dts: zynq: Prepare Parallella

Hi Andreas,

On Thu, Jul 24, 2014 at 4:00 PM, Andreas Färber <afaerber@xxxxxxx> wrote:
> Hello,
>
> This patch series adds an initial device tree for the Parallella board.
> UART, SD card, Ethernet are enabled.
> Not yet enabled are HDMI, QSPI flash and 2x USB.

Andreas (Olofsson) kindly sent me a board, and I added it to the boot
farm today, it'll be included in boot reports from here on.

I did a test run with yesterday's -next It looks like networking isn't
working there at the moment, clock related. Same happens with 3.17 and
latest mainline, config multi_v7_defconfig:

[WARN] [    7.943648] macb e000b000.ethernet eth0: unable to generate
target frequency: 125000000 Hz
[WARN] [   10.948681] macb e000b000.ethernet eth0: unable to generate
target frequency: 125000000 Hz

Full boot log at:

http://arm-soc.lixom.net/bootlogs/misc/next-20141017/parallella-arm-multi_v7_defconfig.html

I'll be happy to try things, but I'm a bit short on cycles to debug
myself. Should hopefully be easy to reproduce.


-Olof
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