* [PATCH v3] clk: imx: Add audio PLL debugfs for K-divider control
@ 2026-06-04 13:48 Jacky Bai
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From: Jacky Bai @ 2026-06-04 13:48 UTC (permalink / raw)
To: Abel Vesa, Peng Fan, Michael Turquette, Stephen Boyd,
Brian Masney, Frank Li, Sascha Hauer, Pengutronix Kernel Team,
Fabio Estevam
Cc: linux-clk, imx, linux-arm-kernel, Jacky Bai
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
Signed-off-by: Jacky Bai <ping.bai@nxp•com>
---
Changes in v3:
- update the spinlock scope based on the Sashiko AI and Peng's comment
- Link to v2: https://lore.kernel.org/r/20260519-imx8m_pll_debugfs-v2-1-20e1d88526b0@nxp.com
Changes in v2:
- remove the examples from commit log.
- refine the comments blocks
- add delta_k read back support
- resolve the comments from Sashiko AI
- add prefix to audio_pll_debug_init API
- Link to v1: https://lore.kernel.org/r/20260512-imx8m_pll_debugfs-v1-1-e1e44b21be90@nxp.com
---
drivers/clk/imx/clk-imx8mm.c | 6 +++
drivers/clk/imx/clk-pll14xx.c | 119 +++++++++++++++++++++++++++++++++++++++++-
drivers/clk/imx/clk.h | 1 +
3 files changed, 125 insertions(+), 1 deletion(-)
diff --git a/drivers/clk/imx/clk-imx8mm.c b/drivers/clk/imx/clk-imx8mm.c
index 319af4deec01c188524807d39dff92bbd08f3601..89d442415a0108ec9b8af85946403b2612ec4fc7 100644
--- a/drivers/clk/imx/clk-imx8mm.c
+++ b/drivers/clk/imx/clk-imx8mm.c
@@ -300,6 +300,7 @@ static int imx8mm_clocks_probe(struct platform_device *pdev)
{
struct device *dev = &pdev->dev;
struct device_node *np = dev->of_node;
+ struct clk_hw *audio_pll_hws[2];
void __iomem *base;
int ret;
@@ -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];
+ imx_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..b6f1cc9f570059b7a1e3d1f9655fa40477c75bb7 100644
--- a/drivers/clk/imx/clk-pll14xx.c
+++ b/drivers/clk/imx/clk-pll14xx.c
@@ -8,11 +8,13 @@
#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>
#include <linux/iopoll.h>
#include <linux/slab.h>
+#include <linux/spinlock.h>
#include <linux/jiffies.h>
#include "clk.h"
@@ -40,6 +42,8 @@ struct clk_pll14xx {
enum imx_pll14xx_type type;
const struct imx_pll14xx_rate_table *rate_table;
int rate_count;
+ s16 delta_k;
+ spinlock_t lock;
};
#define to_clk_pll14xx(_hw) container_of(_hw, struct clk_pll14xx, hw)
@@ -134,6 +138,7 @@ static void imx_pll14xx_calc_settings(struct clk_pll14xx *pll, unsigned long rat
u32 pll_div_ctl0, pll_div_ctl1;
int mdiv, pdiv, sdiv, kdiv;
long fout, rate_min, rate_max, dist, best = LONG_MAX;
+ unsigned long flags;
const struct imx_pll14xx_rate_table *tt;
/*
@@ -161,11 +166,16 @@ static void imx_pll14xx_calc_settings(struct clk_pll14xx *pll, unsigned long rat
return;
}
+ spin_lock_irqsave(&pll->lock, flags);
+
pll_div_ctl0 = readl_relaxed(pll->base + DIV_CTL0);
+ pll_div_ctl1 = readl_relaxed(pll->base + DIV_CTL1);
+
+ spin_unlock_irqrestore(&pll->lock, flags);
+
mdiv = FIELD_GET(MDIV_MASK, pll_div_ctl0);
pdiv = FIELD_GET(PDIV_MASK, pll_div_ctl0);
sdiv = FIELD_GET(SDIV_MASK, pll_div_ctl0);
- pll_div_ctl1 = readl_relaxed(pll->base + DIV_CTL1);
/* Then see if we can get the desired rate by only adjusting kdiv (glitch free) */
rate_min = pll14xx_calc_rate(pll, mdiv, pdiv, sdiv, KDIV_MIN, prate);
@@ -361,11 +371,14 @@ static int clk_pll1443x_set_rate(struct clk_hw *hw, unsigned long drate,
{
struct clk_pll14xx *pll = to_clk_pll14xx(hw);
struct imx_pll14xx_rate_table rate;
+ unsigned long flags;
u32 gnrl_ctl, div_ctl0;
int ret;
imx_pll14xx_calc_settings(pll, drate, prate, &rate);
+ spin_lock_irqsave(&pll->lock, flags);
+
div_ctl0 = readl_relaxed(pll->base + DIV_CTL0);
if (!clk_pll14xx_mp_change(&rate, div_ctl0)) {
@@ -377,6 +390,8 @@ static int clk_pll1443x_set_rate(struct clk_hw *hw, unsigned long drate,
writel_relaxed(FIELD_PREP(KDIV_MASK, rate.kdiv),
pll->base + DIV_CTL1);
+ spin_unlock_irqrestore(&pll->lock, flags);
+
return 0;
}
@@ -396,6 +411,8 @@ static int clk_pll1443x_set_rate(struct clk_hw *hw, unsigned long drate,
writel_relaxed(FIELD_PREP(KDIV_MASK, rate.kdiv), pll->base + DIV_CTL1);
+ spin_unlock_irqrestore(&pll->lock, flags);
+
/*
* According to SPEC, t3 - t2 need to be greater than
* 1us and 1/FREF, respectively.
@@ -508,6 +525,8 @@ struct clk_hw *imx_dev_clk_hw_pll14xx(struct device *dev, const char *name,
if (!pll)
return ERR_PTR(-ENOMEM);
+ spin_lock_init(&pll->lock);
+
init.name = name;
init.flags = pll_clk->flags;
init.parent_names = &parent_name;
@@ -551,3 +570,101 @@ 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): Adjust the K-divider by a small delta_k
+ * echo 1 > /sys/kernel/debug/audio_pll_monitor/audio_pll1/delta_k;
+ */
+#ifdef CONFIG_DEBUG_FS
+static int pll_delta_k_get(void *data, u64 *val)
+{
+ struct clk_pll14xx *pll = to_clk_pll14xx(data);
+ *val = pll->delta_k;
+ return 0;
+}
+
+static int pll_delta_k_set(void *data, u64 val)
+{
+ struct clk_pll14xx *pll = to_clk_pll14xx(data);
+ unsigned long flags;
+ u32 div_ctl1;
+ s16 kdiv, delta_k;
+
+ delta_k = (s16)clamp_t(s64, val, KDIV_MIN, KDIV_MAX);
+
+ spin_lock_irqsave(&pll->lock, flags);
+
+ pll->delta_k = delta_k;
+
+ div_ctl1 = readl_relaxed(pll->base + DIV_CTL1);
+ kdiv = (s16)FIELD_GET(KDIV_MASK, div_ctl1);
+ kdiv = (s16)clamp_t(s32, (s32)kdiv + delta_k, KDIV_MIN, KDIV_MAX);
+ writel_relaxed(FIELD_PREP(KDIV_MASK, kdiv), pll->base + DIV_CTL1);
+
+ spin_unlock_irqrestore(&pll->lock, flags);
+
+ return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE_SIGNED(delta_k_fops, pll_delta_k_get, pll_delta_k_set, "%lld\n");
+
+static int pll_setting_show(struct seq_file *s, void *data)
+{
+ struct clk_pll14xx *pll = to_clk_pll14xx(s->private);
+ unsigned long flags;
+ u32 div_ctl0, div_ctl1;
+ u32 mdiv, pdiv, sdiv, kdiv;
+
+ spin_lock_irqsave(&pll->lock, flags);
+
+ div_ctl0 = readl_relaxed(pll->base + DIV_CTL0);
+ div_ctl1 = readl_relaxed(pll->base + DIV_CTL1);
+
+ spin_unlock_irqrestore(&pll->lock, flags);
+
+ 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 imx_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++) {
+ if (!IS_ERR_OR_NULL(hws[i])) {
+ pll_name = clk_hw_get_name(hws[i]);
+ audio_pll_dir = debugfs_create_dir(pll_name, rootdir);
+ debugfs_create_file_unsafe("delta_k", 0600, 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 imx_audio_pll_debug_init(struct clk_hw *hws[], unsigned int num_plls)
+{
+}
+#endif /* CONFIG_DEBUG_FS */
+EXPORT_SYMBOL_GPL(imx_audio_pll_debug_init);
diff --git a/drivers/clk/imx/clk.h b/drivers/clk/imx/clk.h
index aa5202f284f3d1b7c1b4bf65e2329831832b43a5..40bb41e353f93bf54a6c1b2b6c458f8a65d5845e 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 imx_audio_pll_debug_init(struct clk_hw *hws[], unsigned int num_plls);
#endif
---
base-commit: a225caacc36546a09586e3ece36c0313146e7da9
change-id: 20260421-imx8m_pll_debugfs-246d0fbbb617
Best regards,
--
Jacky Bai <ping.bai@nxp•com>
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