[PATCH net-next v5 0/4] dwmac-meson8b: clock fixes for Meson8b

[Martin Blumenstingl]

Hi Yixun,

On Thu, Jan 18, 2018 at 11:27 AM, Yixun Lan <yixun.lan at amlogic.com> wrote:
> HI Jerome
>
> On 01/17/18 01:19, Jerome Brunet wrote:
>> On Tue, 2018-01-16 at 12:17 +0100, Martin Blumenstingl wrote:
>>>>> Hi Martin
>>>>>
>>>>>   I'm having problem with this series applied.
>>>>> I've tested on the A113D (AXG) platform, if this patch is applied, the
>>>>> driver will choose MPLL2 as clk source, and seems it doesn't work out
>>>>> with this clk (fail to get IP)
>>>>>
>>>>> grep mpll2 /sys/kernel/debug/clk/clk_summary
>>>>>         mpll2                              1            1   249999449
>>>>>       0 0
>>>>>
>>>>
>>>> This is because the fixed pll is 1992000000 on the axg instead of 2Ghz.
>>>
>>> is there a chance that we can have a public AXG datasheet, similar to
>>> what Hardkernel and Khadas published for the S805, S905, S905X and
>>> S912?
>>> this would give us community developers a chance to know that we are
>>> going to break something on AXG *before* a patch is published (like in
>>> this case :( )
>>>
>>>> As a consequence fdiv4 is 498000000.
>>
>> Quick update
>> I have just been able measure fdiv4 and it is exactly 500Mhz
>> This means the the fixed_pll is actually 2GHz, as we would expect.
>>
> yes, you right here. the output of fixed pll is actually 2GHz (1999.998MHz)
>
>
>> This also means that calculation of the fixed_pll is slightly off on the axg
>> platform.
>>
> the calculation algorithm should be updated because previous one didn't
> take the 'frac' part into account.
>
>
>> Once the clock calculation is done correctly on axg, there should be no problem.
>>
> there is still a problem, current calculation will still result at
> fixed_pll frequency - 1999,000,000, I would expect it 2000,000,000 (to
> round it to closest? or just 1999,998,000)
if I understand Jerome's "clk: meson: pll fixes" [0] series correctly
then this should result in a fixed_pll frequency of 1999.998MHz as it
addresses the fractional part as well as the issue where all bits
lower than 1MHz were set to 0

>
>>>>
>>>> CCF can reach something closer to 250Mhz with the mpll2.
>>>>
>>>> The easy way to fix this would be to make the inputs of ethernet mux optional
>>>> and not provide the MPLL2 on the axg.
>>>>
>>>> However, this raises a few question on the axg platform :
>>>> 1) Why is the root pll 1992Mhz and not 2GHz ? seems a weird choice just for 4MHz
>>>> This 1992Mhz does not seems to help generate audio freqs anymore than 2GHz
>>>> would. I don't really get this choice. Could you help us understand Yixun ?
>>>>
>>>> 2) Why is ethernet not working with mpll2 on axg ? espcially since we have
>>>> proven the rate be correct on meson8 ... is there any change on this platform we
>>>> don't know about ?
>>>
>>> I tried to force my Khadas VIM2 (GXM) into using MPLL2 by changing
>>> meson-gxl.dtsi:
>>>         clocks = <&clkc CLKID_ETH>,
>>> -                <&clkc CLKID_FCLK_DIV2>,
>>> +                <&xtal>,
>>>                 <&clkc CLKID_MPLL2>;
>>>
>>> the resulting clock tree looks fine:
>>>     fixed_pll                         4        4        0  2000000000
>>>         0 0
>>>       mpll2_div                      1        1        0   250000000
>>>        0 0
>>>          mpll2                       1        1        0   250000000
>>>        0 0
>>>             c9410000.ethernet#m250_sel       1        1        0
>>> 250000000          0 0
>>>                c9410000.ethernet#m250_div       1        1        0
>>> 250000000          0 0
>>>                   c9410000.ethernet#fixed_div2       1        1
>>> 0   125000000          0 0
>>>                      c9410000.ethernet#rgmii_tx_en       1        1
>>>     0   125000000          0 0
>>>
>>> however, Ethernet is broken (I can't ping anything)
>>>
>>> @Yixun: according to all public datasheets bit 4 is reserved
>>> however, Mike and Kevin were told that bit 4 controls a mux between
>>> FCLK_DIV2 and MPLL2
>>> could you please clarify the meaning of this bit 4 on:
>>> - Meson8b
>>> - Meson8m2 (a confirmation that it uses the same Ethernet registers
>>> with the same bits/meanings of these as Meson8b would be enough)
>>> - GXBB / GXL / GXM (assuming that these are using an identical IP for PRG_ETH0)
>>> - AXG
>>
>> Indeed, if bit 4 stands for something else, or if some combination are known to
>> fail, it would be nice to know.
>>
> the bit 4 is acutally a mux which used to choose two clock sources:
>   a) fclk_div2  b) MPLL2
> (I couldn't check all the SoC generation, but a least I know..)
thank you for clarifying this (which means we do NOT need a patch
which removes the m250_mux from dwmac-meson8b)!

>>>From my point of view, the problem reported by yixun is with the clock
>> controller, not this series, which I think should be merged.
>>
> feedback from ASIC team, they think the MPLL2 clock source should also
> work.. I don't know why it's broken here)-(
is the ASIC team looking into this issue?
maybe it's a simple pinmux issue
if it's broken (and can't be fixed without shipping new hardware) then
maybe we should make the dwmac-meson8b driver aware of it (otherwise
we run into the issues you've been seeing on the AXG platform)


Regards
Martin


[0] http://lists.infradead.org/pipermail/linux-amlogic/2018-January/006204.html