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

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Message-ID: <1516123172.2608.96.camel@baylibre.com>
Date:   Tue, 16 Jan 2018 18:19:32 +0100
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     Yixun Lan <yixun.lan@...ogic.com>, davem@...emloft.net,
        netdev@...r.kernel.org, ingrassia@...genesys.com,
        linus.luessing@...3.blue, Neil Armstrong <narmstrong@...libre.com>,
        khilman@...libre.com, alexandre.torgue@...com,
        linux-amlogic@...ts.infradead.org, peppe.cavallaro@...com
Subject: Re: [PATCH net-next v5 0/4] dwmac-meson8b: clock fixes for Meson8b

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.

This also means that calculation of the fixed_pll is slightly off on the axg
platform.

Once the clock calculation is done correctly on axg, there should be no problem.

> > 
> > 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.

>From my point of view, the problem reported by yixun is with the clock
controller, not this series, which I think should be merged.

Still, we should clockin of the mac optional so don't have to provide the inputs
known to fail, if any.

> 
> 
> Regards
> Martin