Re: [PATCH] clk: imx: Add audio PLL debugfs for K-divider control

[Frank Li <Frank.li@nxp.com>]

On Tue, May 12, 2026 at 05:08:10PM +0800, Jacky Bai wrote:
> Add debugfs support for runtime tuning of the audio PLL K divider,
> which enables fine-grained frequency adjustments for audio PLL.
> This is used for:
>   - Audio clock calibration and testing
>   - Debugging audio synchronization issues
>
> Two debug interfaces are exported to userspace:
>   - delta_k: It is used to adjust the K divider in PLL based on small
>     steps
>   - pll_parameter: It is used for get PLL's current M-divider,
>     P-divider, S-divider & K-divider setting in PLL register
>
> examples for the usage of the two interfaces:
>    1): Get the current PLL setting of dividers
>      cat /sys/kernel/debug/audio_pll_monitor/audio_pll1/pll_parameter
>
>    2): if want to adjust the K-divider by a delta_k '1', then
>      echo 1 > /sys/kernel/debug/audio_pll_monitor/audio_pll1/delta_k;
>
>    3): if want to adjust the K-divider by a delta_k '-1', then
>      echo -1 > /sys/kernel/debug/audio_pll_monitor/audio_pll1/delta_k;

Nit: needn't example, it is basic usage mode for debugfs.

>
> Signed-off-by: Jacky Bai <ping.bai@nxp.com>
> ---
>  drivers/clk/imx/clk-imx8mm.c  |  6 ++++
>  drivers/clk/imx/clk-pll14xx.c | 79 +++++++++++++++++++++++++++++++++++++++++++
>  drivers/clk/imx/clk.h         |  1 +
>  3 files changed, 86 insertions(+)
>
> diff --git a/drivers/clk/imx/clk-imx8mm.c b/drivers/clk/imx/clk-imx8mm.c
> index 319af4deec01c188524807d39dff92bbd08f3601..6a031d7cd031c8b5f5b01e5531ce54360724ba44 100644
> --- a/drivers/clk/imx/clk-imx8mm.c
> +++ b/drivers/clk/imx/clk-imx8mm.c
> @@ -298,6 +298,7 @@ static struct clk_hw **hws;
>
>  static int imx8mm_clocks_probe(struct platform_device *pdev)
>  {
> +	struct clk_hw *audio_pll_hws[2];
>  	struct device *dev = &pdev->dev;
>  	struct device_node *np = dev->of_node;
>  	void __iomem *base;
> @@ -610,6 +611,11 @@ static int imx8mm_clocks_probe(struct platform_device *pdev)
>
>  	imx_register_uart_clocks();
>
> +	/* Add debug interface for audio PLLs */
> +	audio_pll_hws[0] = hws[IMX8MM_AUDIO_PLL1];
> +	audio_pll_hws[1] = hws[IMX8MM_AUDIO_PLL2];
> +	audio_pll_debug_init(audio_pll_hws, ARRAY_SIZE(audio_pll_hws));
> +
>  	return 0;
>
>  unregister_hws:
> diff --git a/drivers/clk/imx/clk-pll14xx.c b/drivers/clk/imx/clk-pll14xx.c
> index 39600ee22be3066683b562aa6f2a8b750d19c4cc..59f126f35474116bdad0aeda59777b9eb7f246cf 100644
> --- a/drivers/clk/imx/clk-pll14xx.c
> +++ b/drivers/clk/imx/clk-pll14xx.c
> @@ -8,6 +8,7 @@
>  #include <linux/bitfield.h>
>  #include <linux/bits.h>
>  #include <linux/clk-provider.h>
> +#include <linux/debugfs.h>
>  #include <linux/err.h>
>  #include <linux/export.h>
>  #include <linux/io.h>
> @@ -551,3 +552,81 @@ struct clk_hw *imx_dev_clk_hw_pll14xx(struct device *dev, const char *name,
>  	return hw;
>  }
>  EXPORT_SYMBOL_GPL(imx_dev_clk_hw_pll14xx);
> +
> +/*
> + * Debugfs interface for Audio PLL runtime monitoring and control
> + *
> + * This interface allows dynamic adjustment of the Audio PLL
> + * K-divider for precise frequency tuning, particularly useful
> + * for audio applications.
> + *
> + * examples for the usage of the two interfaces:
> + *   1): Get the current PLL setting of dividers
> + *     cat /sys/kernel/debug/audio_pll_monitor/audio_pll1/pll_parameter
> + *
> + *   2): if want to adjust the K-divider by a delta_k '1', then
> + *     echo 1 > /sys/kernel/debug/audio_pll_monitor/audio_pll1/delta_k;
> + *
> + *   3): if want to adjust the K-divider by a delta_k '-1', then
> + *     echo -1 > /sys/kernel/debug/audio_pll_monitor/audio_pll1/delta_k;
> + */

2) and 3) keep one is enough, you better descript validate range for
delta_k here, which is more valuable information.

> +#ifdef CONFIG_DEBUG_FS
> +static int pll_delta_k_set(void *data, u64 val)
> +{
> +	struct clk_pll14xx *pll = to_clk_pll14xx(data);
> +	s16 delta_k = (s16)val;
> +	u32 div_ctl1;
> +	s16 kdiv;
> +
> +	div_ctl1 = readl_relaxed(pll->base + DIV_CTL1);
> +	kdiv = FIELD_GET(KDIV_MASK, div_ctl1) + delta_k;
> +	writel_relaxed(FIELD_PREP(KDIV_MASK, kdiv), pll->base + DIV_CTL1);
> +
> +	return 0;
> +}
> +DEFINE_DEBUGFS_ATTRIBUTE_SIGNED(delta_k_fops, NULL, pll_delta_k_set, "%lld\n");

generally, better also provide read for delta_k

cat /sys/kernel/debug/audio_pll_monitor/audio_pll1/delta_k because user
want to check value by read it back naturally.

Frank
> +
> +static int pll_setting_show(struct seq_file *s, void *data)
> +{
> +	struct clk_pll14xx *pll = to_clk_pll14xx(s->private);
> +	u32 div_ctl0, div_ctl1;
> +	u32 mdiv, pdiv, sdiv, kdiv;
> +
> +	div_ctl0 = readl_relaxed(pll->base + DIV_CTL0);
> +	div_ctl1 = readl_relaxed(pll->base + DIV_CTL1);
> +
> +	mdiv = FIELD_GET(MDIV_MASK, div_ctl0);
> +	pdiv = FIELD_GET(PDIV_MASK, div_ctl0);
> +	sdiv = FIELD_GET(SDIV_MASK, div_ctl0);
> +	kdiv = FIELD_GET(KDIV_MASK, div_ctl1);
> +
> +	seq_printf(s, "Mdiv: 0x%x; Pdiv: 0x%x; Sdiv: 0x%x; Kdiv: 0x%x\n",
> +	mdiv, pdiv, sdiv, kdiv);
> +
> +	return 0;
> +}
> +DEFINE_SHOW_ATTRIBUTE(pll_setting);
> +
> +void audio_pll_debug_init(struct clk_hw *hws[], unsigned int num_plls)
> +{
> +	struct dentry *rootdir, *audio_pll_dir;
> +	const char *pll_name;
> +	int i;
> +
> +	rootdir = debugfs_create_dir("audio_pll_monitor", NULL);
> +
> +	for (i = 0; i < num_plls; i++) {
> +		pll_name = clk_hw_get_name(hws[i]);
> +		audio_pll_dir = debugfs_create_dir(pll_name, rootdir);
> +		debugfs_create_file_unsafe("delta_k", 0200, audio_pll_dir,
> +				hws[i], &delta_k_fops);
> +		debugfs_create_file("pll_parameter", 0444, audio_pll_dir,
> +				hws[i], &pll_setting_fops);
> +	}
> +}
> +#else /* !CONFIG_DEBUG_FS */
> +void audio_pll_debug_init(struct clk_hw *hws[], unsigned int num_plls)
> +{
> +}
> +#endif /* CONFIG_DEBUG_FS */
> +EXPORT_SYMBOL_GPL(audio_pll_debug_init);
> diff --git a/drivers/clk/imx/clk.h b/drivers/clk/imx/clk.h
> index aa5202f284f3d1b7c1b4bf65e2329831832b43a5..9611ab127dad6f23770c18e22e1acbe2fc22bd4e 100644
> --- a/drivers/clk/imx/clk.h
> +++ b/drivers/clk/imx/clk.h
> @@ -487,4 +487,5 @@ struct clk_hw *imx_clk_gpr_mux(const char *name, const char *compatible,
>  			       u32 reg, const char **parent_names,
>  			       u8 num_parents, const u32 *mux_table, u32 mask);
>
> +void audio_pll_debug_init(struct clk_hw **hws, unsigned int num_plls);
>  #endif
>
> ---
> base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
> change-id: 20260421-imx8m_pll_debugfs-246d0fbbb617
>
> Best regards,
> --
> Jacky Bai <ping.bai@nxp.com>
>