[PATCH v3 1/4] i2c: spacemit: configure ILCR for accurate SCL frequency

Troy Mitchell
2025-11-18T06:10:06Z

The SpacemiT I2C controller's SCL (Serial Clock Line) frequency for
master mode operations is determined by the ILCR (I2C Load Count Register).
Previously, the driver relied on the hardware's reset default
values for this register.

The hardware's default ILCR values (SLV=0x156, FLV=0x5d) yield SCL
frequencies lower than intended. For example, with the default
31.5 MHz input clock, these default settings result in an SCL
frequency of approximately 93 kHz (standard mode) when targeting 100 kHz,
and approximately 338 kHz (fast mode) when targeting 400 kHz.
These frequencies are below the 100 kHz/400 kHz nominal speeds.

This patch integrates the SCL frequency management into
the Common Clock Framework (CCF). Specifically, the ILCR register,
which acts as a frequency divider for the SCL clock, is now registered
as a managed clock (scl_clk) within the CCF.

This patch also cleans up unnecessary whitespace
in the included header files.

Reviewed-by: Yixun Lan <dlan@gentoo.org>
Link: https://lore.kernel.org/all/176244506110.1925720.10807118665958896958.b4-ty@kernel.org/ [1]
Signed-off-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
---
This patch was affected by the P1 Kconfig, which caused the maintainer
to revert it.
The current commit is a direct cherry-pick and reserves the original changelog.
This note is to clarify for anyone who sees the cover letter marked as v2
while the changelog entries reach v4.
---
Changelog in v4:
- initialize clk_init_data with {} so that init.flags is implicitly set to 0
- minor cleanup and style fixes for better readability
- remove unused spacemit_i2c_scl_clk_exclusive_put() cleanup callback
- replace clk_set_rate_exclusive()/clk_rate_exclusive_put() pair with clk_set_rate()
- simplify LCR LV field macros by using FIELD_GET/FIELD_MAX helpers
- Link to v3: https://lore.kernel.org/all/20250814-k1-i2c-ilcr-v3-1-317723e74bcd@linux.spacemit.com/

Changelog in v3:
- use MASK macro in `recalc_rate` function
- rename clock name
- Link to v2: https://lore.kernel.org/r/20250718-k1-i2c-ilcr-v2-1-b4c68f13dcb1@linux.spacemit.com

Changelog in v2:
- Align line breaks.
- Check `lv` in `clk_set_rate` function.
- Force fast mode when SCL frequency is illegal or unavailable.
- Change "linux/bits.h" to <linux/bits.h>
- Kconfig: Add dependency on CCF.
- Link to v1: https://lore.kernel.org/all/20250710-k1-i2c-ilcr-v1-1-188d1f460c7d@linux.spacemit.com/
---
drivers/i2c/busses/Kconfig | 2 +-
drivers/i2c/busses/i2c-k1.c | 159 ++++++++++++++++++++++++++++++++++++++++----
2 files changed, 146 insertions(+), 15 deletions(-)

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index fd81e49638aaa161ae264a722e9e06adc7914cda..fedf5d31f9035b73a27a7f8a764bf5c26975d0e1 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -798,7 +798,7 @@ config I2C_JZ4780
config I2C_K1
tristate "SpacemiT K1 I2C adapter"
depends on ARCH_SPACEMIT || COMPILE_TEST
- depends on OF
+ depends on OF && COMMON_CLK
help
This option enables support for the I2C interface on the SpacemiT K1
platform.
diff --git a/drivers/i2c/busses/i2c-k1.c b/drivers/i2c/busses/i2c-k1.c
index 6b918770e612e098b8ad17418f420d87c94df166..e38a0ba71734ca602854c85672dcb61423453515 100644
--- a/drivers/i2c/busses/i2c-k1.c
+++ b/drivers/i2c/busses/i2c-k1.c
@@ -4,18 +4,21 @@
*/

#include <linux/bitfield.h>
- #include <linux/clk.h>
- #include <linux/i2c.h>
- #include <linux/iopoll.h>
- #include <linux/module.h>
- #include <linux/of_address.h>
- #include <linux/platform_device.h>
+#include <linux/bits.h>
+#include <linux/clk.h>
+#include <linux/clk-provider.h>
+#include <linux/i2c.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/of_address.h>
+#include <linux/platform_device.h>

/* spacemit i2c registers */
#define SPACEMIT_ICR 0x0 /* Control register */
#define SPACEMIT_ISR 0x4 /* Status register */
#define SPACEMIT_IDBR 0xc /* Data buffer register */
#define SPACEMIT_IRCR 0x18 /* Reset cycle counter */
+#define SPACEMIT_ILCR 0x10 /* Load Count Register */
#define SPACEMIT_IBMR 0x1c /* Bus monitor register */

/* SPACEMIT_ICR register fields */
@@ -87,6 +90,13 @@
#define SPACEMIT_BMR_SDA BIT(0) /* SDA line level */
#define SPACEMIT_BMR_SCL BIT(1) /* SCL line level */

+#define SPACEMIT_LCR_LV_STANDARD_SHIFT 0
+#define SPACEMIT_LCR_LV_FAST_SHIFT 9
+#define SPACEMIT_LCR_LV_STANDARD_MASK GENMASK(8, 0)
+#define SPACEMIT_LCR_LV_FAST_MASK GENMASK(17, 9)
+#define SPACEMIT_LCR_LV_STANDARD_MAX_VALUE FIELD_MAX(SPACEMIT_LCR_LV_STANDARD_MASK)
+#define SPACEMIT_LCR_LV_FAST_MAX_VALUE FIELD_MAX(SPACEMIT_LCR_LV_FAST_MASK)
+
/* i2c bus recover timeout: us */
#define SPACEMIT_I2C_BUS_BUSY_TIMEOUT 100000

@@ -104,11 +114,20 @@ enum spacemit_i2c_state {
SPACEMIT_STATE_WRITE,
};

+enum spacemit_i2c_mode {
+ SPACEMIT_MODE_STANDARD,
+ SPACEMIT_MODE_FAST
+};
+
/* i2c-spacemit driver's main struct */
struct spacemit_i2c_dev {
struct device *dev;
struct i2c_adapter adapt;

+ struct clk_hw scl_clk_hw;
+ struct clk *scl_clk;
+ enum spacemit_i2c_mode mode;
+
/* hardware resources */
void __iomem *base;
int irq;
@@ -129,6 +148,79 @@ struct spacemit_i2c_dev {
u32 status;
};

+static void spacemit_i2c_scl_clk_disable_unprepare(void *data)
+{
+ struct spacemit_i2c_dev *i2c = data;
+
+ clk_disable_unprepare(i2c->scl_clk);
+}
+
+static int spacemit_i2c_clk_set_rate(struct clk_hw *hw, unsigned long rate,
+ unsigned long parent_rate)
+{
+ struct spacemit_i2c_dev *i2c = container_of(hw, struct spacemit_i2c_dev, scl_clk_hw);
+ u32 lv, lcr, mask, shift, max_lv;
+
+ lv = DIV_ROUND_UP(parent_rate, rate);
+
+ if (i2c->mode == SPACEMIT_MODE_STANDARD) {
+ mask = SPACEMIT_LCR_LV_STANDARD_MASK;
+ shift = SPACEMIT_LCR_LV_STANDARD_SHIFT;
+ max_lv = SPACEMIT_LCR_LV_STANDARD_MAX_VALUE;
+ } else if (i2c->mode == SPACEMIT_MODE_FAST) {
+ mask = SPACEMIT_LCR_LV_FAST_MASK;
+ shift = SPACEMIT_LCR_LV_FAST_SHIFT;
+ max_lv = SPACEMIT_LCR_LV_FAST_MAX_VALUE;
+ }
+
+ if (!lv || lv > max_lv) {
+ dev_err(i2c->dev, "set scl clock failed: lv 0x%x", lv);
+ return -EINVAL;
+ }
+
+ lcr = readl(i2c->base + SPACEMIT_ILCR);
+ lcr &= ~mask;
+ lcr |= lv << shift;
+ writel(lcr, i2c->base + SPACEMIT_ILCR);
+
+ return 0;
+}
+
+static long spacemit_i2c_clk_round_rate(struct clk_hw *hw, unsigned long rate,
+ unsigned long *parent_rate)
+{
+ u32 lv, freq;
+
+ lv = DIV_ROUND_UP(*parent_rate, rate);
+ freq = DIV_ROUND_UP(*parent_rate, lv);
+
+ return freq;
+}
+
+static unsigned long spacemit_i2c_clk_recalc_rate(struct clk_hw *hw,
+ unsigned long parent_rate)
+{
+ struct spacemit_i2c_dev *i2c = container_of(hw, struct spacemit_i2c_dev, scl_clk_hw);
+ u32 lcr, lv = 0;
+
+ lcr = readl(i2c->base + SPACEMIT_ILCR);
+
+ if (i2c->mode == SPACEMIT_MODE_STANDARD)
+ lv = FIELD_GET(SPACEMIT_LCR_LV_STANDARD_MASK, lcr);
+ else if (i2c->mode == SPACEMIT_MODE_FAST)
+ lv = FIELD_GET(SPACEMIT_LCR_LV_FAST_MASK, lcr);
+ else
+ return 0;
+
+ return DIV_ROUND_UP(parent_rate, lv);
+}
+
+static const struct clk_ops spacemit_i2c_clk_ops = {
+ .set_rate = spacemit_i2c_clk_set_rate,
+ .round_rate = spacemit_i2c_clk_round_rate,
+ .recalc_rate = spacemit_i2c_clk_recalc_rate,
+};
+
static void spacemit_i2c_enable(struct spacemit_i2c_dev *i2c)
{
u32 val;
@@ -147,6 +239,26 @@ static void spacemit_i2c_disable(struct spacemit_i2c_dev *i2c)
writel(val, i2c->base + SPACEMIT_ICR);
}

+static struct clk *spacemit_i2c_register_scl_clk(struct spacemit_i2c_dev *i2c,
+ struct clk *parent)
+{
+ struct clk_init_data init = {};
+ char name[32];
+
+ snprintf(name, sizeof(name), "%s_scl_clk", dev_name(i2c->dev));
+
+ init.name = name;
+ init.ops = &spacemit_i2c_clk_ops;
+ init.parent_data = (struct clk_parent_data[]) {
+ { .fw_name = "func" },
+ };
+ init.num_parents = 1;
+
+ i2c->scl_clk_hw.init = &init;
+
+ return devm_clk_register(i2c->dev, &i2c->scl_clk_hw);
+}
+
static void spacemit_i2c_reset(struct spacemit_i2c_dev *i2c)
{
writel(SPACEMIT_CR_UR, i2c->base + SPACEMIT_ICR);
@@ -246,7 +358,7 @@ static void spacemit_i2c_init(struct spacemit_i2c_dev *i2c)
*/
val |= SPACEMIT_CR_DRFIE;

- if (i2c->clock_freq == SPACEMIT_I2C_MAX_FAST_MODE_FREQ)
+ if (i2c->mode == SPACEMIT_MODE_FAST)
val |= SPACEMIT_CR_MODE_FAST;

/* disable response to general call */
@@ -538,14 +650,15 @@ static int spacemit_i2c_probe(struct platform_device *pdev)
dev_warn(dev, "failed to read clock-frequency property: %d\n", ret);

/* For now, this driver doesn't support high-speed. */
- if (!i2c->clock_freq || i2c->clock_freq > SPACEMIT_I2C_MAX_FAST_MODE_FREQ) {
- dev_warn(dev, "unsupported clock frequency %u; using %u\n",
- i2c->clock_freq, SPACEMIT_I2C_MAX_FAST_MODE_FREQ);
+ if (i2c->clock_freq > SPACEMIT_I2C_MAX_STANDARD_MODE_FREQ &&
+ i2c->clock_freq <= SPACEMIT_I2C_MAX_FAST_MODE_FREQ) {
+ i2c->mode = SPACEMIT_MODE_FAST;
+ } else if (i2c->clock_freq && i2c->clock_freq <= SPACEMIT_I2C_MAX_STANDARD_MODE_FREQ) {
+ i2c->mode = SPACEMIT_MODE_STANDARD;
+ } else {
+ dev_warn(i2c->dev, "invalid clock-frequency, fallback to fast mode");
+ i2c->mode = SPACEMIT_MODE_FAST;
i2c->clock_freq = SPACEMIT_I2C_MAX_FAST_MODE_FREQ;
- } else if (i2c->clock_freq < SPACEMIT_I2C_MAX_STANDARD_MODE_FREQ) {
- dev_warn(dev, "unsupported clock frequency %u; using %u\n",
- i2c->clock_freq, SPACEMIT_I2C_MAX_STANDARD_MODE_FREQ);
- i2c->clock_freq = SPACEMIT_I2C_MAX_STANDARD_MODE_FREQ;
}

i2c->dev = &pdev->dev;
@@ -567,10 +680,28 @@ static int spacemit_i2c_probe(struct platform_device *pdev)
if (IS_ERR(clk))
return dev_err_probe(dev, PTR_ERR(clk), "failed to enable func clock");

+ i2c->scl_clk = spacemit_i2c_register_scl_clk(i2c, clk);
+ if (IS_ERR(i2c->scl_clk))
+ return dev_err_probe(&pdev->dev, PTR_ERR(i2c->scl_clk),
+ "failed to register scl clock\n");
+
clk = devm_clk_get_enabled(dev, "bus");
if (IS_ERR(clk))
return dev_err_probe(dev, PTR_ERR(clk), "failed to enable bus clock");

+ ret = clk_set_rate(i2c->scl_clk, i2c->clock_freq);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret, "failed to set rate for SCL clock");
+
+ ret = clk_prepare_enable(i2c->scl_clk);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret, "failed to prepare and enable clock");
+
+ ret = devm_add_action_or_reset(dev, spacemit_i2c_scl_clk_disable_unprepare, i2c);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret,
+ "failed to register cleanup action for clk disable and unprepare");
+
spacemit_i2c_reset(i2c);

i2c_set_adapdata(&i2c->adapt, i2c);

--
2.51.2