Re: [PATCH V1 3/3] ARM: imx6q: Add the clock route from external OSC to ESAI clock

[Shawn Guo <shawn.guo@freescale.com>]

On Mon, Aug 04, 2014 at 07:11:15PM +0800, Shengjiu Wang wrote:
> This patch mainly adds the clock route from external 24.576MHz OSC to internal
> ESAI clock via analog clock2 PADs on the SoC and pll4 so that ESAI can get an
> entirely synchronous clock source against CS42888.
> 
> [ 1, We found if using pll4 to generate a 24.576MHz from inernal 24.0MHz OSC,
>   we would get noise during the audio playback via ESAI->CS42888 even though
>   this generated clock's rate is equal to the external one statistically. It
>   might be resulted from the tiny difference between two clock source, which
>   might be crucial to the sensitive CODEC we use -- CS42888. So we here apply
>   the old 3.0.35 way to feed ESAI the same clock source as CS42888.
> 
>   2, Ideally, we should use bypass mode for pll4 since we only need to get
>   the raw rate (24.576MHz) while currently bypass mode in clk-pllv3.c isn't
>   entirely supported: The clock rate would be fixed to 24.0MHz if setting to
>   bypass, which would cause child clock get an incorrect rate and the driver
>   who uses the child clock fail to derive a needed clock rate, and it might
>   be dangerous to involve the clk-pllv3.c driver to this fix. Thus we here
>   apply 3.0.35 way provisionally. ]

Instead of hacking it around, I consider it's time to properly implement
PLL bypass mode.  It's essentially just another multiplexer.

Shawn

> 
>   Expected result:
> 
>   anaclk2                 0           1            24576000
>    lvds2_in               0           1            24576000
>     pll4_sel              0           1            24576000
>      pll4_audio           0           1            786432000
>       pll4_post_div       0           1            786432000
>        pll4_audio_div     0           1            786432000
>         esai_sel          0           1            786432000
>          esai_pred        0           1            98304000
>           esai_podf       0           1            24576000
>            esai           0           1            24576000
> 
> Signed-off-by: Nicolin Chen <Guangyu.Chen@freescale.com>
> Signed-off-by: Shengjiu Wang <shengjiu.wang@freescale.com>
> ---
>  arch/arm/mach-imx/clk-imx6q.c  |    5 +++++
>  arch/arm/mach-imx/mach-imx6q.c |   28 ++++++++++++++++++++++++++++
>  2 files changed, 33 insertions(+)
> 
> diff --git a/arch/arm/mach-imx/clk-imx6q.c b/arch/arm/mach-imx/clk-imx6q.c
> index 927a062..2d3634f 100644
> --- a/arch/arm/mach-imx/clk-imx6q.c
> +++ b/arch/arm/mach-imx/clk-imx6q.c
> @@ -413,6 +413,10 @@ static void __init imx6q_clocks_init(struct device_node *ccm_node)
>  	of_clk_add_provider(np, of_clk_src_onecell_get, &clk_data);
>  
>  	clk_register_clkdev(clk[IMX6QDL_CLK_ENET_REF], "enet_ref", NULL);
> +	clk_register_clkdev(clk[IMX6QDL_CLK_PLL4_AUDIO_DIV], "pll4_audio_div", NULL);
> +	clk_register_clkdev(clk[IMX6QDL_CLK_PLL4_SEL], "pll4_sel", NULL);
> +	clk_register_clkdev(clk[IMX6QDL_CLK_LVDS2_IN], "lvds2_in", NULL);
> +	clk_register_clkdev(clk[IMX6QDL_CLK_ESAI_EXTAL], "esai_extal", NULL);
>  
>  	if ((imx_get_soc_revision() != IMX_CHIP_REVISION_1_0) ||
>  	    cpu_is_imx6dl()) {
> @@ -456,6 +460,7 @@ static void __init imx6q_clocks_init(struct device_node *ccm_node)
>  
>  	/* Audio-related clocks configuration */
>  	clk_set_parent(clk[IMX6QDL_CLK_SPDIF_SEL], clk[IMX6QDL_CLK_PLL3_PFD3_454M]);
> +	clk_set_parent(clk[IMX6QDL_CLK_ESAI_SEL], clk[IMX6QDL_CLK_PLL4_AUDIO_DIV]);
>  
>  	/* All existing boards with PCIe use LVDS1 */
>  	if (IS_ENABLED(CONFIG_PCI_IMX6))
> diff --git a/arch/arm/mach-imx/mach-imx6q.c b/arch/arm/mach-imx/mach-imx6q.c
> index d51c6e9..ea24a96 100644
> --- a/arch/arm/mach-imx/mach-imx6q.c
> +++ b/arch/arm/mach-imx/mach-imx6q.c
> @@ -362,6 +362,28 @@ put_node:
>  	of_node_put(np);
>  }
>  
> +#define ESAI_AUDIO_MCLK 24576000
> +
> +static void __init imx6q_audio_lvds2_init(void)
> +{
> +        struct clk *pll4_sel, *lvds2_in, *pll4_audio_div, *esai_extal;
> +
> +        pll4_audio_div = clk_get_sys(NULL, "pll4_audio_div");
> +        pll4_sel = clk_get_sys(NULL, "pll4_sel");
> +        lvds2_in = clk_get_sys(NULL, "lvds2_in");
> +        esai_extal = clk_get_sys(NULL, "esai_extal");
> +        if (IS_ERR(pll4_audio_div) || IS_ERR(pll4_sel) ||
> +            IS_ERR(lvds2_in) || IS_ERR(esai_extal))
> +                return;
> +
> +        if (clk_get_rate(lvds2_in) != ESAI_AUDIO_MCLK)
> +                return;
> +
> +        clk_set_parent(pll4_sel, lvds2_in);
> +        clk_set_rate(pll4_audio_div, 786432000);
> +        clk_set_rate(esai_extal, ESAI_AUDIO_MCLK);
> +}
> +
>  static struct platform_device imx6q_cpufreq_pdev = {
>  	.name = "imx6q-cpufreq",
>  };
> @@ -379,6 +401,12 @@ static void __init imx6q_init_late(void)
>  		imx6q_opp_init();
>  		platform_device_register(&imx6q_cpufreq_pdev);
>  	}
> +
> +	if (of_machine_is_compatible("fsl,imx6q-sabreauto")
> +		|| of_machine_is_compatible("fsl,imx6dl-sabreauto")) {
> +		imx6q_audio_lvds2_init();
> +	}
> +
>  }
>  
>  static void __init imx6q_map_io(void)
> -- 
> 1.7.9.5
>