Re: [PATCH v6 5/8] clk: clock-wizard: Add support for fractional support

From: Stephen Boyd
Date: Mon Sep 21 2020 - 17:17:42 EST

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Quoting Shubhrajyoti Datta (2020-08-28 06:39:53)
> Currently the set rate granularity is to integral divisors.
> Add support for the fractional divisors.
> Only the first output0 is fractional in the hardware.
>
> Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xxxxxxxxxx>

Getting closer.

> diff --git a/drivers/clk/clk-xlnx-clock-wizard.c b/drivers/clk/clk-xlnx-clock-wizard.c
> index 8dfcec8..1af59a4 100644
> --- a/drivers/clk/clk-xlnx-clock-wizard.c
> +++ b/drivers/clk/clk-xlnx-clock-wizard.c
> @@ -185,6 +191,134 @@ static const struct clk_ops clk_wzrd_clk_divider_ops = {
> .recalc_rate = clk_wzrd_recalc_rate,
> };
>
> +static unsigned long clk_wzrd_recalc_ratef(struct clk_hw *hw,
> + unsigned long parent_rate)
> +{
> + unsigned int val;
> + u32 div, frac;
> + struct clk_wzrd_divider *divider = to_clk_wzrd_divider(hw);
> + void __iomem *div_addr = divider->base + divider->offset;
> +
> + val = readl(div_addr);
> + div = val & div_mask(divider->width);
> + frac = (val >> WZRD_CLKOUT_FRAC_SHIFT) & WZRD_CLKOUT_FRAC_MASK;
> +
> + return ((parent_rate * 1000) / ((div * 1000) + frac));

Please remove extra parenthesis. And is this mult_frac()?

> +}
> +
> +static int clk_wzrd_dynamic_reconfig_f(struct clk_hw *hw, unsigned long rate,
> + unsigned long parent_rate)
> +{
> + int err;
> + u32 value, pre;
> + unsigned long rate_div, f, clockout0_div;
> + struct clk_wzrd_divider *divider = to_clk_wzrd_divider(hw);
> + void __iomem *div_addr = divider->base + divider->offset;
> +
> + rate_div = ((parent_rate * 1000) / rate);
> + clockout0_div = rate_div / 1000;
> +
> + pre = DIV_ROUND_CLOSEST((parent_rate * 1000), rate);
> + f = (u32)(pre - (clockout0_div * 1000));
> + f = f & WZRD_CLKOUT_FRAC_MASK;
> +
> + value = ((f << WZRD_CLKOUT_DIVIDE_WIDTH) | (clockout0_div &
> + WZRD_CLKOUT_DIVIDE_MASK));

Please split this to multiple lines.

> +
> + /* Set divisor and clear phase offset */
> + writel(value, div_addr);
> + writel(0x0, div_addr + WZRD_DR_DIV_TO_PHASE_OFFSET);
> +
> + /* Check status register */
> + err= readl_poll_timeout(divider->base + WZRD_DR_STATUS_REG_OFFSET, value,
> + value & WZRD_DR_LOCK_BIT_MASK,
> + WZRD_USEC_POLL, WZRD_TIMEOUT_POLL);
> + if (err)
> + return err;
> +
> + /* Initiate reconfiguration */
> + writel(WZRD_DR_BEGIN_DYNA_RECONF,
> + divider->base + WZRD_DR_INIT_REG_OFFSET);
> +
> + /* Check status register */
> + err= readl_poll_timeout(divider->base + WZRD_DR_STATUS_REG_OFFSET, value,
> + value & WZRD_DR_LOCK_BIT_MASK,
> + WZRD_USEC_POLL, WZRD_TIMEOUT_POLL);
> +
> + return err;

Just return readl_poll_timeout() please.

> +}
> +
> +static long clk_wzrd_round_rate_f(struct clk_hw *hw, unsigned long rate,
> + unsigned long *prate)
> +{
> + return rate;

Can every rate be supported? This function is supposed to tell the clk
framework what rate will be achieved if we call clk_set_rate() with
'rate' passed to this function. Almost always returning 'rate' is not
the case.

>
> +
> +static const struct clk_ops clk_wzrd_clk_divider_ops_f = {
> + .round_rate = clk_wzrd_round_rate_f,
> + .set_rate = clk_wzrd_dynamic_reconfig_f,
> + .recalc_rate = clk_wzrd_recalc_ratef,
> +};
> +
> +static struct clk *clk_wzrd_register_divf(struct device *dev,
> + const char *name,
> + const char *parent_name,
> + unsigned long flags,
> + void __iomem *base, u16 offset,
> + u8 shift, u8 width,
> + u8 clk_divider_flags,
> + const struct clk_div_table *table,
> + spinlock_t *lock)
> +{
> + struct clk_wzrd_divider *div;
> + struct clk_hw *hw;
> + struct clk_init_data init;
> + int ret;
> +
> + if (clk_divider_flags & CLK_DIVIDER_HIWORD_MASK) {

Is this used? It's a rockchip specific flag mostly so probably not?

> + if (width + shift > 16) {
> + pr_warn("divider value exceeds LOWORD field\n");
> + return ERR_PTR(-EINVAL);
> + }
> + }
> +
> + /* allocate the divider */

Please remove useless comments like this.

> + div = kzalloc(sizeof(*div), GFP_KERNEL);
> + if (!div)
> + return ERR_PTR(-ENOMEM);
> +
> + init.name = name;
> +
> + if (clk_divider_flags & CLK_DIVIDER_READ_ONLY)

Is this flag used?

> + init.ops = &clk_divider_ro_ops;
> + else
> + init.ops = &clk_wzrd_clk_divider_ops_f;
> +
> + init.flags = flags;
> + init.parent_names = (parent_name ? &parent_name : NULL);
> + init.num_parents = (parent_name ? 1 : 0);

Do you have cases where there isn't a parent? Hopefully not, so this
can be simplified.

>
> + /* struct clk_divider assignments */

Drop this comment?

> + div->base = base;
> + div->offset = offset;
> + div->shift = shift;
> + div->width = width;
> + div->flags = clk_divider_flags;
> + div->lock = lock;
> + div->hw.init = &init;
> + div->table = table;
> +
> + /* register the clock */

Drop this comment?

> + hw = &div->hw;
> + ret = clk_hw_register(dev, hw);

Any reason we can't use devm_clk_hw_register() here?

> + if (ret) {
> + kfree(div);
> + return ERR_PTR(ret);
> + }
> +
> + return hw->clk;
> +}
> +
> static struct clk *clk_wzrd_register_divider(struct device *dev,
> const char *name,
> const char *parent_name,
> @@ -355,17 +489,13 @@ static int clk_wzrd_probe(struct platform_device *pdev)
> goto err_disable_clk;
> }
>
> - /* we don't support fractional div/mul yet */
> - reg = readl(clk_wzrd->base + WZRD_CLK_CFG_REG(0)) &
> - WZRD_CLKFBOUT_FRAC_EN;
> - reg |= readl(clk_wzrd->base + WZRD_CLK_CFG_REG(2)) &
> - WZRD_CLKOUT0_FRAC_EN;
> - if (reg)
> - dev_warn(&pdev->dev, "fractional div/mul not supported\n");
> -
> /* register multiplier */
> reg = (readl(clk_wzrd->base + WZRD_CLK_CFG_REG(0)) &
> WZRD_CLKFBOUT_MULT_MASK) >> WZRD_CLKFBOUT_MULT_SHIFT;
> + reg_f = (readl(clk_wzrd->base + WZRD_CLK_CFG_REG(0)) &
> + WZRD_CLKFBOUT_FRAC_MASK) >> WZRD_CLKFBOUT_FRAC_SHIFT;

Use two lines please. Read into variable on one line, shift on another.

> +
> + mult = ((reg * 1000) + reg_f);

Please remove extra parenthesis.

> clk_name = kasprintf(GFP_KERNEL, "%s_mul", dev_name(&pdev->dev));
> if (!clk_name) {
> ret = -ENOMEM;
> @@ -413,8 +543,18 @@ static int clk_wzrd_probe(struct platform_device *pdev)
> ret = -EINVAL;
> goto err_rm_int_clks;
> }
> - clk_wzrd->clkout[i] = clk_wzrd_register_divider(&pdev->dev,
> - clkout_name,
> + if (!i)
> + clk_wzrd->clkout[i] = clk_wzrd_register_divf
> + (&pdev->dev, clkout_name,
> + clk_name, 0,
> + clk_wzrd->base, (WZRD_CLK_CFG_REG(2) + i * 12),
> + WZRD_CLKOUT_DIVIDE_SHIFT,
> + WZRD_CLKOUT_DIVIDE_WIDTH,
> + CLK_DIVIDER_ONE_BASED | CLK_DIVIDER_ALLOW_ZERO,
> + NULL, &clkwzrd_lock);
> + else
> + clk_wzrd->clkout[i] = clk_wzrd_register_divider
> + (&pdev->dev, clkout_name,
> clk_name, 0,
> clk_wzrd->base, (WZRD_CLK_CFG_REG(2) + i * 12),
> WZRD_CLKOUT_DIVIDE_SHIFT,
>

I wonder if a do-while loop with flags set to ONE_BASED and ALLOW_ZERO
could work and then flags gets overwritten to be just DIVIDE_SHIFT? Then
we don't have to duplicate the registration line.

Next message: Peter Xu: "[PATCH 0/5] mm: Break COW for pinned pages during fork()"
Previous message: Colin King: "[PATCH][V2][next] PCI: brcmstb: fix a missing if statement on a return error check"
Next in thread: Dan Carpenter: "Re: [PATCH v6 5/8] clk: clock-wizard: Add support for fractional support"
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