linux-kernel - Re: [PATCH 2/8] clk: tegra: host1x has fractional divider

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Message-ID: <20180723085010.GK1636@tbergstrom-lnx.Nvidia.com>
Date:   Mon, 23 Jul 2018 11:50:10 +0300
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Ben Dooks <ben.dooks@...ethink.co.uk>
CC:     <linux-clk@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <pgaikwad@...dia.com>,
        <jonathanh@...dia.co>, <thierry.reding@...il.com>,
        <linux-kernel@...ts.codethink.co.uk>
Subject: Re: [PATCH 2/8] clk: tegra: host1x has fractional divider

On Fri, Jul 20, 2018 at 02:45:26PM +0100, Ben Dooks wrote:
> The host1x clock according to both tegra2 and tegra3 manuals is
> an 8bit divider with lsb being fractional. This is running into
> an issue where the host1x is being set on a tegra20a system to
> 266.4MHz but ends up at 222MHz instead.
> 

The fact the hw has a fractional divider, does not mean we're allowed to use
it. Due to the non 50% duty cycle of fractional divided clocks, they are not
allowed for certain peripherals. Do you have information indicating this is
ok for the host1x clock?

Peter.


> Signed-off-by: Ben Dooks <ben.dooks@...ethink.co.uk>
> ---
>  drivers/clk/tegra/clk-tegra-periph.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/tegra/clk-tegra-periph.c b/drivers/clk/tegra/clk-tegra-periph.c
> index 2acba2986bc6..8fa1cecf18a0 100644
> --- a/drivers/clk/tegra/clk-tegra-periph.c
> +++ b/drivers/clk/tegra/clk-tegra-periph.c
> @@ -644,7 +644,7 @@ static struct tegra_periph_init_data periph_clks[] = {
>  	INT("vde", mux_pllp_pllc_pllm_clkm, CLK_SOURCE_VDE, 61, 0, tegra_clk_vde),
>  	INT("vi", mux_pllm_pllc_pllp_plla, CLK_SOURCE_VI, 20, 0, tegra_clk_vi),
>  	INT("epp", mux_pllm_pllc_pllp_plla, CLK_SOURCE_EPP, 19, 0, tegra_clk_epp),
> -	INT("host1x", mux_pllm_pllc_pllp_plla, CLK_SOURCE_HOST1X, 28, 0, tegra_clk_host1x),
> +	MUX("host1x", mux_pllm_pllc_pllp_plla, CLK_SOURCE_HOST1X, 28, 0, tegra_clk_host1x),
>  	INT("mpe", mux_pllm_pllc_pllp_plla, CLK_SOURCE_MPE, 60, 0, tegra_clk_mpe),
>  	INT("2d", mux_pllm_pllc_pllp_plla, CLK_SOURCE_2D, 21, 0, tegra_clk_gr2d),
>  	INT("3d", mux_pllm_pllc_pllp_plla, CLK_SOURCE_3D, 24, 0, tegra_clk_gr3d),
> -- 
> 2.18.0
>