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Subject: Re: [PATCH 1/7] clk: qcom: add support for setting the duty cycle
To:     Brian Masney <masneyb@onstation.org>, sboyd@kernel.org,
        dmitry.torokhov@gmail.com, robh+dt@kernel.org
Cc:     mark.rutland@arm.com, agross@kernel.org,
        bjorn.andersson@linaro.org, mturquette@baylibre.com,
        linux-input@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-clk@vger.kernel.org
References: <20191205002503.13088-1-masneyb@onstation.org>
 <20191205002503.13088-2-masneyb@onstation.org>
From:   Taniya Das <tdas@codeaurora.org>
Message-ID: <0101016eee224b83-b0577d24-8f51-4e1a-9afb-b3f518e5ba77-000000@us-west-2.amazonses.com>
Date:   Tue, 10 Dec 2019 04:47:35 +0000
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Hi Brian,

On 12/5/2019 5:54 AM, Brian Masney wrote:
> Add support for setting the duty cycle via the D register for the
> Qualcomm clocks.
> 
> Signed-off-by: Brian Masney <masneyb@onstation.org>
> ---
> A few quirks that were noted when varying the speed of CAMSS_GP1_CLK on
> msm8974 (Nexus 5 phone):
> 
>    - The mnd_width is set to 8 bits, however the d width is actually 7
>      bits, at least for this clock. I'm not sure about the other clocks.
> 
>    - When the d register has a value less than 17, the following error
>      from update_config() is shown: rcg didn't update its configuration.
>      So this patch keeps the value of the d register within the range
>      [17, 127].
> 
> I'm not sure about the relationship of the m, n, and d values,
> especially how the 50% duty cycle is calculated by inverting the n
> value, so that's why I'm saving the duty cycle ratio for
> get_duty_cycle().
> 
>   drivers/clk/qcom/clk-rcg.h  |  4 +++
>   drivers/clk/qcom/clk-rcg2.c | 61 +++++++++++++++++++++++++++++++++++--
>   2 files changed, 63 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/qcom/clk-rcg.h b/drivers/clk/qcom/clk-rcg.h
> index 78358b81d249..c3b8732cec8f 100644
> --- a/drivers/clk/qcom/clk-rcg.h
> +++ b/drivers/clk/qcom/clk-rcg.h
> @@ -139,6 +139,8 @@ extern const struct clk_ops clk_dyn_rcg_ops;
>    * @freq_tbl: frequency table
>    * @clkr: regmap clock handle
>    * @cfg_off: defines the cfg register offset from the CMD_RCGR + CFG_REG
> + * @duty_cycle_num: Numerator of the duty cycle ratio
> + * @duty_cycle_den: Denominator of the duty cycle ratio
>    */
>   struct clk_rcg2 {
>   	u32			cmd_rcgr;
> @@ -149,6 +151,8 @@ struct clk_rcg2 {
>   	const struct freq_tbl	*freq_tbl;
>   	struct clk_regmap	clkr;
>   	u8			cfg_off;
> +	int			duty_cycle_num;
> +	int			duty_cycle_den;
>   };
>   
>   #define to_clk_rcg2(_hw) container_of(to_clk_regmap(_hw), struct clk_rcg2, clkr)
> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> index 8f4b9bec2956..8d685baefe50 100644
> --- a/drivers/clk/qcom/clk-rcg2.c
> +++ b/drivers/clk/qcom/clk-rcg2.c
> @@ -258,7 +258,11 @@ static int clk_rcg2_determine_floor_rate(struct clk_hw *hw,
>   	return _freq_tbl_determine_rate(hw, rcg->freq_tbl, req, FLOOR);
>   }
>   
> -static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
> +static int __clk_rcg2_configure_with_duty_cycle(struct clk_rcg2 *rcg,
> +						const struct freq_tbl *f,
> +						int d_reg_val,
> +						int duty_cycle_num,
> +						int duty_cycle_den)
>   {
>   	u32 cfg, mask;
>   	struct clk_hw *hw = &rcg->clkr.hw;
> @@ -280,9 +284,12 @@ static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
>   			return ret;
>   
>   		ret = regmap_update_bits(rcg->clkr.regmap,
> -				RCG_D_OFFSET(rcg), mask, ~f->n);
> +				RCG_D_OFFSET(rcg), mask, d_reg_val);
>   		if (ret)
>   			return ret;
> +
> +		rcg->duty_cycle_num = duty_cycle_num;
> +		rcg->duty_cycle_den = duty_cycle_den;
>   	}
>   
>   	mask = BIT(rcg->hid_width) - 1;
> @@ -295,6 +302,12 @@ static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
>   					mask, cfg);
>   }
>   
> +static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
> +{
> +	/* Set a 50% duty cycle */
> +	return __clk_rcg2_configure_with_duty_cycle(rcg, f, ~f->n, 1, 2);
> +}
> +
>   static int clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
>   {
>   	int ret;
> @@ -353,6 +366,32 @@ static int clk_rcg2_set_floor_rate_and_parent(struct clk_hw *hw,
>   	return __clk_rcg2_set_rate(hw, rate, FLOOR);
>   }
>   
> +static int clk_rcg2_get_duty_cycle(struct clk_hw *hw, struct clk_duty *duty)
> +{
> +	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> +
> +	duty->num = rcg->duty_cycle_num;
> +	duty->den = rcg->duty_cycle_den;
> +
> +	return 0;
> +}
> +
> +static int clk_rcg2_set_duty_cycle(struct clk_hw *hw, struct clk_duty *duty)
> +{
> +	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
> +	int ret, d_reg_val, mask;
> +
> +	mask = BIT(rcg->mnd_width - 1) - 1;
> +	d_reg_val = mask - (((mask - 17) * duty->num) / duty->den);
> +	ret = __clk_rcg2_configure_with_duty_cycle(rcg, rcg->freq_tbl,
> +						   d_reg_val, duty->num,
> +						   duty->den);

The duty-cycle calculation is not accurate.
There is already a plan to submit the duty-cycle changes from my side.
> +	if (ret)
> +		return ret;
> +
> +	return update_config(rcg);
> +}
> +
>   const struct clk_ops clk_rcg2_ops = {
>   	.is_enabled = clk_rcg2_is_enabled,
>   	.get_parent = clk_rcg2_get_parent,
> @@ -361,6 +400,8 @@ const struct clk_ops clk_rcg2_ops = {
>   	.determine_rate = clk_rcg2_determine_rate,
>   	.set_rate = clk_rcg2_set_rate,
>   	.set_rate_and_parent = clk_rcg2_set_rate_and_parent,
> +	.get_duty_cycle = clk_rcg2_get_duty_cycle,
> +	.set_duty_cycle = clk_rcg2_set_duty_cycle,
>   };
>   EXPORT_SYMBOL_GPL(clk_rcg2_ops);
>   
> @@ -372,6 +413,8 @@ const struct clk_ops clk_rcg2_floor_ops = {
>   	.determine_rate = clk_rcg2_determine_floor_rate,
>   	.set_rate = clk_rcg2_set_floor_rate,
>   	.set_rate_and_parent = clk_rcg2_set_floor_rate_and_parent,
> +	.get_duty_cycle = clk_rcg2_get_duty_cycle,
> +	.set_duty_cycle = clk_rcg2_set_duty_cycle,
>   };
>   EXPORT_SYMBOL_GPL(clk_rcg2_floor_ops);
>   
> @@ -499,6 +542,8 @@ const struct clk_ops clk_edp_pixel_ops = {
>   	.set_rate = clk_edp_pixel_set_rate,
>   	.set_rate_and_parent = clk_edp_pixel_set_rate_and_parent,
>   	.determine_rate = clk_edp_pixel_determine_rate,
> +	.get_duty_cycle = clk_rcg2_get_duty_cycle,
> +	.set_duty_cycle = clk_rcg2_set_duty_cycle,
>   };
>   EXPORT_SYMBOL_GPL(clk_edp_pixel_ops);
>   
> @@ -557,6 +602,8 @@ const struct clk_ops clk_byte_ops = {
>   	.set_rate = clk_byte_set_rate,
>   	.set_rate_and_parent = clk_byte_set_rate_and_parent,
>   	.determine_rate = clk_byte_determine_rate,
> +	.get_duty_cycle = clk_rcg2_get_duty_cycle,
> +	.set_duty_cycle = clk_rcg2_set_duty_cycle,
>   };
>   EXPORT_SYMBOL_GPL(clk_byte_ops);
>   
> @@ -627,6 +674,8 @@ const struct clk_ops clk_byte2_ops = {
>   	.set_rate = clk_byte2_set_rate,
>   	.set_rate_and_parent = clk_byte2_set_rate_and_parent,
>   	.determine_rate = clk_byte2_determine_rate,
> +	.get_duty_cycle = clk_rcg2_get_duty_cycle,
> +	.set_duty_cycle = clk_rcg2_set_duty_cycle,
>   };
>   EXPORT_SYMBOL_GPL(clk_byte2_ops);
>   
> @@ -717,6 +766,8 @@ const struct clk_ops clk_pixel_ops = {
>   	.set_rate = clk_pixel_set_rate,
>   	.set_rate_and_parent = clk_pixel_set_rate_and_parent,
>   	.determine_rate = clk_pixel_determine_rate,
> +	.get_duty_cycle = clk_rcg2_get_duty_cycle,
> +	.set_duty_cycle = clk_rcg2_set_duty_cycle,
>   };
>   EXPORT_SYMBOL_GPL(clk_pixel_ops);
>   
> @@ -804,6 +855,8 @@ const struct clk_ops clk_gfx3d_ops = {
>   	.set_rate = clk_gfx3d_set_rate,
>   	.set_rate_and_parent = clk_gfx3d_set_rate_and_parent,
>   	.determine_rate = clk_gfx3d_determine_rate,
> +	.get_duty_cycle = clk_rcg2_get_duty_cycle,
> +	.set_duty_cycle = clk_rcg2_set_duty_cycle,
>   };
>   EXPORT_SYMBOL_GPL(clk_gfx3d_ops);
>   
> @@ -942,6 +995,8 @@ const struct clk_ops clk_rcg2_shared_ops = {
>   	.determine_rate = clk_rcg2_determine_rate,
>   	.set_rate = clk_rcg2_shared_set_rate,
>   	.set_rate_and_parent = clk_rcg2_shared_set_rate_and_parent,
> +	.get_duty_cycle = clk_rcg2_get_duty_cycle,
> +	.set_duty_cycle = clk_rcg2_set_duty_cycle,
>   };
>   EXPORT_SYMBOL_GPL(clk_rcg2_shared_ops);
>   
> @@ -1081,6 +1136,8 @@ static const struct clk_ops clk_rcg2_dfs_ops = {
>   	.get_parent = clk_rcg2_get_parent,
>   	.determine_rate = clk_rcg2_dfs_determine_rate,
>   	.recalc_rate = clk_rcg2_dfs_recalc_rate,
> +	.get_duty_cycle = clk_rcg2_get_duty_cycle,
> +	.set_duty_cycle = clk_rcg2_set_duty_cycle,
>   };
> 

Why do you want to support duty-cycle for other RCGs when you are 
specifically want it for GP clocks only.
The DFS can never handle duty-cycle set/get.

>   static int clk_rcg2_enable_dfs(const struct clk_rcg_dfs_data *data,
> 

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