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Date:   Mon, 12 Mar 2018 11:14:07 +0200
From:   Peter De Schrijver <pdeschrijver@nvidia.com>
To:     Jon Hunter <jonathanh@nvidia.com>
CC:     <linux-tegra@vger.kernel.org>, <linux-clk@vger.kernel.org>,
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Subject: Re: [PATCH v3 05/11] clk: tegra: prepare dfll driver for PWM
 regulator
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On Thu, Mar 08, 2018 at 10:50:06PM +0000, Jon Hunter wrote:
> 
> On 06/02/18 16:34, Peter De Schrijver wrote:
> > This patch prepares the dfll driver to work with PWM regulators.
> > To do this we introduce a new array lut_uv which gives the voltage for
> > a given index generated by the dfll logic. This index will then be
> > translated to a PMIC voltage ID in case of I2C using the i2c_lut. In case
> > of a PWM regulator, it will be used to determine the PWM duty cycle.
> > We also introduce lut_bottom which holds the lowest voltage we will ever
> > need. In case of I2C this can be set to zero because the i2c_lut will be
> > initialized such that entry 0 will be the lowest voltage we will ever
> > need. In case of PWM, the lowest voltage is determined by the regulator
> > hardware so we need this software limit. Note that this is different
> > from lut_min which gives the lowest voltage we allow taking temperature
> > into account. In a future patchset we will update lut_vmin dynamically.
> > Similarly lut_max will be the highest voltage allowed taking temperature
> > into accouint. Also this will be updated dynamically once temperature
> > dependence will be introduced.
> > 
> > Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
> > ---
> >  drivers/clk/tegra/clk-dfll.c | 62 ++++++++++++++++++++++++++------------------
> >  1 file changed, 37 insertions(+), 25 deletions(-)
> > 
> > diff --git a/drivers/clk/tegra/clk-dfll.c b/drivers/clk/tegra/clk-dfll.c
> > index 0a7deee..fa97763 100644
> > --- a/drivers/clk/tegra/clk-dfll.c
> > +++ b/drivers/clk/tegra/clk-dfll.c
> > @@ -301,9 +301,10 @@ struct tegra_dfll {
> >  	u32				i2c_slave_addr;
> >  
> >  	/* i2c_lut array entries are regulator framework selectors */
> > -	unsigned			i2c_lut[MAX_DFLL_VOLTAGES];
> > -	int				i2c_lut_size;
> > -	u8				lut_min, lut_max, lut_safe;
> > +	unsigned int			i2c_lut[MAX_DFLL_VOLTAGES];
> > +	unsigned int			lut_uv[MAX_DFLL_VOLTAGES];
> > +	int				lut_size;
> > +	u8				lut_bottom, lut_min, lut_max, lut_safe;
> >  };
> >  
> >  #define clk_hw_to_dfll(_hw) container_of(_hw, struct tegra_dfll, dfll_clk_hw)
> > @@ -531,10 +532,10 @@ static void dfll_load_i2c_lut(struct tegra_dfll *td)
> >  	u32 val;
> >  
> >  	for (i = 0; i < MAX_DFLL_VOLTAGES; i++) {
> > -		if (i < td->lut_min)
> > -			lut_index = td->lut_min;
> > -		else if (i > td->lut_max)
> > -			lut_index = td->lut_max;
> > +		if (i < td->lut_bottom)
> > +			lut_index = td->lut_bottom;
> > +		else if (i > td->lut_size - 1)
> > +			lut_index = td->lut_size - 1;
> >  		else
> >  			lut_index = i;
> >  
> > @@ -594,9 +595,9 @@ static void dfll_init_out_if(struct tegra_dfll *td)
> >  {
> >  	u32 val;
> >  
> > -	td->lut_min = 0;
> > -	td->lut_max = td->i2c_lut_size - 1;
> > -	td->lut_safe = td->lut_min + 1;
> > +	td->lut_min = td->lut_bottom;
> > +	td->lut_max = td->lut_size - 1;
> > +	td->lut_safe = td->lut_min + (td->lut_min < td->lut_max ? 1 : 0);
> >  
> >  	dfll_i2c_writel(td, 0, DFLL_OUTPUT_CFG);
> >  	val = (td->lut_safe << DFLL_OUTPUT_CFG_SAFE_SHIFT) |
> > @@ -619,11 +620,11 @@ static void dfll_init_out_if(struct tegra_dfll *td)
> >   */
> >  
> >  /**
> > - * find_lut_index_for_rate - determine I2C LUT index for given DFLL rate
> > + * find_lut_index_for_rate - determine LUT index for given DFLL rate
> >   * @td: DFLL instance
> >   * @rate: clock rate
> >   *
> > - * Determines the index of a I2C LUT entry for a voltage that approximately
> > + * Determines the index of a LUT entry for a voltage that approximately
> >   * produces the given DFLL clock rate. This is used when forcing a value
> >   * to the integrator during rate changes. Returns -ENOENT if a suitable
> >   * LUT index is not found.
> > @@ -637,11 +638,11 @@ static int find_lut_index_for_rate(struct tegra_dfll *td, unsigned long rate)
> >  	if (IS_ERR(opp))
> >  		return PTR_ERR(opp);
> >  
> > -	uv = dev_pm_opp_get_voltage(opp);
> > +	uv = dev_pm_opp_get_voltage(opp) / td->soc->alignment.step_uv;
> >  	dev_pm_opp_put(opp);
> >  
> > -	for (i = 0; i < td->i2c_lut_size; i++) {
> > -		if (regulator_list_voltage(td->vdd_reg, td->i2c_lut[i]) == uv)
> > +	for (i = td->lut_bottom; i < td->lut_size; i++) {
> > +		if ((td->lut_uv[i] / td->soc->alignment.step_uv) >= uv)
> >  			return i;
> >  	}
> >  
> > @@ -1377,15 +1378,17 @@ static int dfll_init(struct tegra_dfll *td)
> >   */
> >  static int find_vdd_map_entry_exact(struct tegra_dfll *td, int uV)
> >  {
> > -	int i, n_voltages, reg_uV;
> > +	int i, n_voltages, reg_mult, align_mult;
> >  
> > +	align_mult = uV / td->soc->alignment.step_uv;
> >  	n_voltages = regulator_count_voltages(td->vdd_reg);
> >  	for (i = 0; i < n_voltages; i++) {
> > -		reg_uV = regulator_list_voltage(td->vdd_reg, i);
> > -		if (reg_uV < 0)
> > +		reg_mult = regulator_list_voltage(td->vdd_reg, i) /
> > +				td->soc->alignment.step_uv;
> > +		if (reg_mult < 0)
> >  			break;
> >  
> > -		if (uV == reg_uV)
> > +		if (align_mult == reg_mult)
> >  			return i;
> >  	}
> >  
> > @@ -1399,15 +1402,17 @@ static int find_vdd_map_entry_exact(struct tegra_dfll *td, int uV)
> >   * */
> >  static int find_vdd_map_entry_min(struct tegra_dfll *td, int uV)
> >  {
> > -	int i, n_voltages, reg_uV;
> > +	int i, n_voltages, reg_mult, align_mult;
> >  
> > +	align_mult = uV / td->soc->alignment.step_uv;
> >  	n_voltages = regulator_count_voltages(td->vdd_reg);
> >  	for (i = 0; i < n_voltages; i++) {
> > -		reg_uV = regulator_list_voltage(td->vdd_reg, i);
> > -		if (reg_uV < 0)
> > +		reg_mult = regulator_list_voltage(td->vdd_reg, i) /
> > +				td->soc->alignment.step_uv;
> > +		if (reg_mult < 0)
> >  			break;
> >  
> > -		if (uV <= reg_uV)
> > +		if (align_mult <= reg_mult)
> >  			return i;
> >  	}
> >  
> > @@ -1450,8 +1455,10 @@ static int dfll_build_i2c_lut(struct tegra_dfll *td)
> >  	if (lut < 0)
> >  		goto out;
> >  	td->i2c_lut[0] = lut;
> > +	td->lut_bottom = 0;
> >  
> >  	for (j = 1, rate = 0; ; rate++) {
> > +
> >  		opp = dev_pm_opp_find_freq_ceil(td->soc->dev, &rate);
> >  		if (IS_ERR(opp))
> >  			break;
> > @@ -1484,13 +1491,18 @@ static int dfll_build_i2c_lut(struct tegra_dfll *td)
> >  		if (v >= v_max)
> >  			break;
> >  	}
> > -	td->i2c_lut_size = j;
> > +	td->lut_size = j;
> >  
> >  	if (!td->dvco_rate_min)
> >  		dev_err(td->dev, "no opp above DFLL minimum voltage %d mV\n",
> >  			td->soc->cvb->min_millivolts);
> > -	else
> > +	else {
> >  		ret = 0;
> > +		for (j = 0; j < td->lut_size; j++)
> > +			td->lut_uv[j] =
> > +				regulator_list_voltage(td->vdd_reg,
> > +						       td->i2c_lut[j]);
> > +	}
> >  
> >  out:
> >  	return ret;
> > 
> 
> I am a bit confused by this patch as I don't fully understand from the
> description what is being changed. For example, there are a few places
> where you are dividing by td->soc->alignment.step_uv, which seems to be
> changing the calculations/behaviour for I2C unless I am missing something?
> 

The goal is to use td->lut_uv for all voltage related lookups so we can unify
the code for i2c and PWM regulators.

Peter.

> I would also consider renaming lut_bottom and lut_min as something like
> lut_abs_min and lut_cur_min, to indicate that one is the absolute min
> and the other is the current min depending on operating conditions.
> 
> Cheers
> Jon
> 
> -- 
> nvpublic