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Message-ID: <20250928110327-GYA1346428@gentoo.org>
Date: Sun, 28 Sep 2025 19:03:27 +0800
From: Yixun Lan <dlan@...too.org>
To: Troy Mitchell <troy.mitchell@...ux.spacemit.com>
Cc: Andi Shyti <andi.shyti@...nel.org>, linux-i2c@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
spacemit@...ts.linux.dev
Subject: Re: [PATCH v3] i2c: spacemit: configure ILCR for accurate SCL
frequency
Hi Troy,
On 17:06 Thu 14 Aug , Troy Mitchell wrote:
> 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.
>
> Signed-off-by: Troy Mitchell <troy.mitchell@...ux.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 | 180 ++++++++++++++++++++++++++++++++++++++++----
> 2 files changed, 167 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index c8d115b58e449b59a38339b439190dcb0e332965..1382b6c257fa4ba4cf5098d684c1bbd5e2636fd4 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -797,7 +797,7 @@ 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 b68a21fff0b56b59fe2032ccb7ca6953423aad32..34b22969cf6789e99de58dd93dda6f0951069f85 100644
> --- a/drivers/i2c/busses/i2c-k1.c
> +++ b/drivers/i2c/busses/i2c-k1.c
> @@ -3,17 +3,20 @@
> * Copyright (C) 2024-2025 Troy Mitchell <troymitchell988@...il.com>
> */
>
> - #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_ILCR 0x10 /* Load Count Register */
> #define SPACEMIT_IBMR 0x1c /* Bus monitor register */
>
> /* SPACEMIT_ICR register fields */
> @@ -80,6 +83,19 @@
> #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_WIDTH 9
> +#define SPACEMIT_LCR_LV_FAST_WIDTH 9
..
> +#define SPACEMIT_LCR_LV_STANDARD_MAX_VALUE GENMASK(SPACEMIT_LCR_LV_STANDARD_WIDTH - 1, 0)
> +#define SPACEMIT_LCR_LV_FAST_MAX_VALUE GENMASK(SPACEMIT_LCR_LV_FAST_WIDTH - 1, 0)
using GENMASK() makes people even confusing since it's not a mask, I would
suggest simply put value directly here, which is 0x1ff
> +#define SPACEMIT_LCR_LV_STANDARD_MASK GENMASK(SPACEMIT_LCR_LV_STANDARD_SHIFT +\
> + SPACEMIT_LCR_LV_STANDARD_WIDTH - 1,\
> + SPACEMIT_LCR_LV_STANDARD_SHIFT)
same reason here, suggest simplify as
#define SPACEMIT_LCR_LV_STANDARD_MASK GENMASK(8, 0)
which is more readable and maintenace friendly
> +#define SPACEMIT_LCR_LV_FAST_MASK GENMASK(SPACEMIT_LCR_LV_FAST_SHIFT +\
> + SPACEMIT_LCR_LV_FAST_WIDTH - 1,\
> + SPACEMIT_LCR_LV_FAST_SHIFT)
> +
..[snip]
> +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;
..
> + init.flags = 0;
I think you can drop this line, by simply init it at declaration
struct clk_init_data init = {};
..
> +
> + 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);
> @@ -224,7 +352,7 @@ 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 */
> @@ -519,14 +647,15 @@ 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, using fast mode");
s/using../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;
> @@ -548,10 +677,33 @@ 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");
you can use dev_err_ptr_probe()
>
> + ret = clk_set_rate_exclusive(i2c->scl_clk, i2c->clock_freq);
why use _exclusive_ API? is there multi consumers? can you explain?
> + if (ret)
> + return dev_err_probe(&pdev->dev, ret, "failed to set exclusive rate for SCL clock");
> +
--
Yixun Lan (dlan)
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