linux-kernel - Re: [PATCH v4 5/7] clk: axi-clkgen: Respect ZYNQMP PFD/VCO frequency limits

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Date:   Wed, 30 Sep 2020 08:22:23 +0300
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Moritz Fischer <mdf@...nel.org>
Cc:     Alexandru Ardelean <alexandru.ardelean@...log.com>,
        linux-clk@...r.kernel.org, linux-fpga@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Mathias Tausen <mta@...space.com>
Subject: Re: [PATCH v4 5/7] clk: axi-clkgen: Respect ZYNQMP PFD/VCO frequency limits

On Tue, Sep 29, 2020 at 6:30 PM Moritz Fischer <mdf@...nel.org> wrote:
>
> Hi Alexandru,
>
> On Tue, Sep 29, 2020 at 05:44:15PM +0300, Alexandru Ardelean wrote:
> > From: Mathias Tausen <mta@...space.com>
> >
> > Since axi-clkgen is now supported on ZYNQMP, make sure the max/min
> > frequencies of the PFD and VCO are respected.
> >
> > Signed-off-by: Mathias Tausen <mta@...space.com>
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
>
> This patch still does not cover the PCIe Zynq plugged into ZynqMP linux
> machine case.
>
> > ---
> >  drivers/clk/clk-axi-clkgen.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/clk/clk-axi-clkgen.c b/drivers/clk/clk-axi-clkgen.c
> > index 4342b7735590..2319bb1c5c08 100644
> > --- a/drivers/clk/clk-axi-clkgen.c
> > +++ b/drivers/clk/clk-axi-clkgen.c
> > @@ -108,12 +108,21 @@ static uint32_t axi_clkgen_lookup_lock(unsigned int m)
> >       return 0x1f1f00fa;
> >  }
> >
> > +#ifdef ARCH_ZYNQMP
> > +static const struct axi_clkgen_limits axi_clkgen_default_limits = {
> > +     .fpfd_min = 10000,
> > +     .fpfd_max = 450000,
> > +     .fvco_min = 800000,
> > +     .fvco_max = 1600000,
> > +};
> > +#else
> >  static const struct axi_clkgen_limits axi_clkgen_default_limits = {
> >       .fpfd_min = 10000,
> >       .fpfd_max = 300000,
> >       .fvco_min = 600000,
> >       .fvco_max = 1200000,
> >  };
> > +#endif
>
> I still don't understand this. You have a way to determine which fabric
> you are looking at with the FPGA info. Why not:
>
> [..] axi_clkgen_zynqmp_default_limits = {
> };
>
> [..] axi_clkgen_default_limits = {
> };
>
> Set them based on what you read back, i.e. determine which fabric you
> are looking at *per clock gen* and use that info, rather than making a
> compile time decision to support only one of them.
>
> Generally speaking #ifdef $ARCH should be a last resort solution.

The support for reading back the fabric parameters is implemented in
the AXI CLKGEN PCORE version starting with 5.0.a
Links:
https://github.com/analogdevicesinc/hdl/commits/master/library/common/up_clkgen.v
https://github.com/analogdevicesinc/hdl/commit/66823682b63c1037abdc3fc1dd4d4e63d3cfbc1a
https://github.com/analogdevicesinc/hdl/commit/7dcb2050c7946fab5ea5a273eda7c53ea7b969a6

Before that version, these details aren't there, so the best you can
do is assume compile-time ARCH defaults.

Looking at patch 7 [in this series], the axi_clkgen only updates these
defaults if the PCORE version is above version 4.x.x
https://lore.kernel.org/linux-clk/20200929144417.89816-16-alexandru.ardelean@analog.com/T/#u

Now, the question would be: do we still support PCORE versions before 5.0.a?
Depending on the answer to this question, I would be fine with the
proposed change here.

> >
> >  static void axi_clkgen_calc_params(const struct axi_clkgen_limits *limits,
> >       unsigned long fin, unsigned long fout,
> > --
> > 2.17.1
> >
>
> Cheers,
> Moritz