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

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Date:   Tue, 29 Sep 2020 08:30:40 -0700
From:   Moritz Fischer <mdf@...nel.org>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     linux-clk@...r.kernel.org, linux-fpga@...r.kernel.org,
        linux-kernel@...r.kernel.org, mturquette@...libre.com,
        sboyd@...nel.org, mdf@...nel.org, ardeleanalex@...il.com,
        Mathias Tausen <mta@...space.com>
Subject: Re: [PATCH v4 5/7] clk: axi-clkgen: Respect ZYNQMP PFD/VCO frequency
 limits

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

Cheers,
Moritz