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Date: Wed, 27 May 2020 16:29:17 +0200
From: Lars Povlsen <lars.povlsen@...rochip.com>
To: Stephen Boyd <sboyd@...nel.org>
CC: Arnd Bergmann <arnd@...db.de>,
Linus Walleij <linus.walleij@...aro.org>,
SoC Team <soc@...nel.org>,
Lars Povlsen <lars.povlsen@...rochip.com>,
"Steen Hegelund" <Steen.Hegelund@...rochip.com>,
Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
Olof Johansson <olof@...om.net>,
"Michael Turquette" <mturquette@...libre.com>,
<devicetree@...r.kernel.org>, <linux-clk@...r.kernel.org>,
<linux-gpio@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>,
Alexandre Belloni <alexandre.belloni@...tlin.com>
Subject: Re: [PATCH 12/14] clk: sparx5: Add Sparx5 SoC DPLL clock driver
Stephen Boyd writes:
> Quoting Lars Povlsen (2020-05-13 05:55:30)
>> diff --git a/drivers/clk/clk-sparx5.c b/drivers/clk/clk-sparx5.c
>> new file mode 100644
>> index 0000000000000..685b3028a7071
>> --- /dev/null
>> +++ b/drivers/clk/clk-sparx5.c
>> @@ -0,0 +1,269 @@
>> +// SPDX-License-Identifier: GPL-2.0-or-later
>> +/*
>> + * Microchip Sparx5 SoC Clock driver.
>> + *
>> + * Copyright (c) 2019 Microchip Inc.
>> + *
>> + * Author: Lars Povlsen <lars.povlsen@...rochip.com>
>> + */
>> +
>> +#include <linux/io.h>
>> +#include <linux/clk-provider.h>
>> +#include <linux/of.h>
>> +#include <linux/of_address.h>
>> +#include <linux/slab.h>
>> +#include <linux/platform_device.h>
>> +#include <dt-bindings/clock/microchip,sparx5.h>
>> +
>> +#define PLL_DIV_MASK GENMASK(7, 0)
>> +#define PLL_PRE_DIV_MASK GENMASK(10, 8)
>> +#define PLL_PRE_DIV_SHIFT 8
>> +#define PLL_ROT_DIR BIT(11)
>> +#define PLL_ROT_SEL_MASK GENMASK(13, 12)
>> +#define PLL_ROT_SEL_SHIFT 12
>> +#define PLL_ROT_ENA BIT(14)
>> +#define PLL_CLK_ENA BIT(15)
>> +
>> +#define MAX_SEL 4
>> +#define MAX_PRE BIT(3)
>> +
>> +#define KHZ 1000
>> +#define MHZ (KHZ*KHZ)
>
> I suspect (1000 * KHZ) would make more sense.
>
Fine.
>> +
>> +#define BASE_CLOCK (2500UL*MHZ)
>> +
>> +static u8 sel_rates[MAX_SEL] = { 0, 2*8, 2*4, 2*2 };
>
> const?
>
Yes, sure.
>> +
>> +static const char *clk_names[N_CLOCKS] = {
>> + "core", "ddr", "cpu2", "arm2",
>> + "aux1", "aux2", "aux3", "aux4",
>> + "synce",
>> +};
>> +
>> +struct s5_hw_clk {
>> + struct clk_hw hw;
>> + void __iomem *reg;
>> + int index;
>> +};
>> +
>> +struct s5_clk_data {
>> + void __iomem *base;
>> + struct s5_hw_clk s5_hw[N_CLOCKS];
>> +};
>> +
>> +struct pll_conf {
>> + int freq;
>> + u8 div;
>> + bool rot_ena;
>> + u8 rot_sel;
>> + u8 rot_dir;
>> + u8 pre_div;
>> +};
>> +
>> +#define to_clk_pll(hw) container_of(hw, struct s5_hw_clk, hw)
>> +
>> +unsigned long calc_freq(const struct pll_conf *pdata)
>> +{
>> + unsigned long rate = BASE_CLOCK / pdata->div;
>> +
>> + if (pdata->rot_ena) {
>> + unsigned long base = BASE_CLOCK / pdata->div;
>> + int sign = pdata->rot_dir ? -1 : 1;
>> + int divt = sel_rates[pdata->rot_sel] * (1 + pdata->pre_div);
>> + int divb = divt + sign;
>> +
>> + rate = mult_frac(base, divt, divb);
>> + rate = roundup(rate, 1000);
>> + }
>> +
>> + return rate;
>> +}
>> +
>> +static unsigned long clk_calc_params(unsigned long rate,
>> + struct pll_conf *conf)
>> +{
>> + memset(conf, 0, sizeof(*conf));
>> +
>> + conf->div = DIV_ROUND_CLOSEST_ULL(BASE_CLOCK, rate);
>> +
>> + if (BASE_CLOCK % rate) {
>> + struct pll_conf best;
>> + ulong cur_offset, best_offset = rate;
>> + int i, j;
>> +
>> + /* Enable fractional rotation */
>> + conf->rot_ena = true;
>> +
>> + if ((BASE_CLOCK / rate) != conf->div) {
>> + /* Overshoot, adjust other direction */
>> + conf->rot_dir = 1;
>> + }
>> +
>> + /* Brute force search over MAX_PRE * (MAX_SEL - 1) = 24 */
>> + for (i = 0; i < MAX_PRE; i++) {
>> + conf->pre_div = i;
>> + for (j = 1; j < MAX_SEL; j++) {
>> + conf->rot_sel = j;
>> + conf->freq = calc_freq(conf);
>> + cur_offset = abs(rate - conf->freq);
>> + if (cur_offset == 0)
>> + /* Perfect fit */
>> + goto done;
>
> Why not 'break' and drop the label?
>
Its a dual loop. Anyway, I changed it to add "best_offset > 0" in the
loop guards and drop "cur_offset == 0" as a special case, so no goto.
>> + if (cur_offset < best_offset) {
>> + /* Better fit found */
>> + best_offset = cur_offset;
>> + best = *conf;
>> + }
>> + }
>> + }
>> + /* Best match */
>> + *conf = best;
>> + }
>> +
>> +done:
>> + return conf->freq;
>> +}
>> +
>> +static int clk_pll_enable(struct clk_hw *hw)
>> +{
>> + struct s5_hw_clk *pll = to_clk_pll(hw);
>> + u32 val = readl(pll->reg);
>> +
>> + val |= PLL_CLK_ENA;
>> + writel(val, pll->reg);
>> + pr_debug("%s: Enable val %04x\n", clk_names[pll->index], val);
>> + return 0;
>> +}
>> +
>> +static void clk_pll_disable(struct clk_hw *hw)
>> +{
>> + struct s5_hw_clk *pll = to_clk_pll(hw);
>> + u32 val = readl(pll->reg);
>> +
>> + val &= ~PLL_CLK_ENA;
>> + writel(val, pll->reg);
>> + pr_debug("%s: Disable val %04x\n", clk_names[pll->index], val);
>
> Can we drop these pr_debug() prints? They're probably never going to be
> used after developing this driver.
>
>> +}
>> +
>> +static int clk_pll_set_rate(struct clk_hw *hw,
>
> Please rename clk_pll to something less generic, like s5_pll or
> something.
>
Yeah, I see that. I changed all generic symbols to use s5_ prefix where
applicable. Also fixed non-static calc_freq() symbol.
>> + unsigned long rate,
>> + unsigned long parent_rate)
>> +{
>> + struct s5_hw_clk *pll = to_clk_pll(hw);
>> + struct pll_conf conf;
>> + unsigned long eff_rate;
>> + int ret = 0;
>> +
>> + eff_rate = clk_calc_params(rate, &conf);
>> + if (eff_rate == rate) {
>> + u32 val;
>> +
>> + val = readl(pll->reg) & PLL_CLK_ENA;
>> + val |= PLL_DIV_MASK & conf.div;
>> + if (conf.rot_ena) {
>> + val |= (PLL_ROT_ENA |
>> + (PLL_ROT_SEL_MASK &
>> + (conf.rot_sel << PLL_ROT_SEL_SHIFT)) |
>> + (PLL_PRE_DIV_MASK &
>> + (conf.pre_div << PLL_PRE_DIV_SHIFT)));
>
> This can use the FIELD_GET and helpers?
>
Yes, makes sense. Done.
>> + if (conf.rot_dir)
>> + val |= PLL_ROT_DIR;
>> + }
>> + pr_debug("%s: Rate %ld >= 0x%04x\n",
>> + clk_names[pll->index], rate, val);
>> + writel(val, pll->reg);
>> + } else {
>> + pr_err("%s: freq unsupported: %ld paren %ld\n",
>> + clk_names[pll->index], rate, parent_rate);
>> + ret = -ENOTSUPP;
>
> I'd prefer we short circuit the function
>
> eff_rate = clk_calc_params(...);
> if (eff_rate != rate)
> return -ENOTSUPP;
>
> do the other things...
>
> This avoids lots of indentation.
Ok, noted.
>
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +static unsigned long clk_pll_recalc_rate(struct clk_hw *hw,
>> + unsigned long parent_rate)
>> +{
>> + /* Don't care */
>
> What does this mean? recalc_rate is supposed to tell us what rate has
> been achieved for this clk.
I added a proper implementation for this.
>
>> + return 0;
>> +}
>> +
>> +static long clk_pll_round_rate(struct clk_hw *hw, unsigned long rate,
>> + unsigned long *parent_rate)
>> +{
>> + struct pll_conf conf;
>> + unsigned long eff_rate;
>> +
>> + eff_rate = clk_calc_params(rate, &conf);
>> + pr_debug("%s: Rate %ld rounded to %ld\n", __func__, rate, eff_rate);
>> +
>> + return eff_rate;
>> +}
>> +
>> +static const struct clk_ops s5_pll_ops = {
>> + .enable = clk_pll_enable,
>> + .disable = clk_pll_disable,
>> + .set_rate = clk_pll_set_rate,
>> + .round_rate = clk_pll_round_rate,
>> + .recalc_rate = clk_pll_recalc_rate,
>> +};
>> +
>> +static struct s5_clk_data *s5_clk_alloc(struct device_node *np)
>> +{
>> + struct s5_clk_data *clk_data;
>> +
>> + clk_data = kzalloc(sizeof(*clk_data), GFP_KERNEL);
>> + if (WARN_ON(!clk_data))
>
> Drop the WARN_ON(), kzalloc() already prints a big stacktrace when it
> fails.
Yes.
>
>> + return NULL;
>> +
>> + clk_data->base = of_iomap(np, 0);
>> + if (WARN_ON(!clk_data->base))
>> + return NULL;
>> +
>> + return clk_data;
>
> Just inline this function at the callsite please.
>
Yes.
>> +}
>> +
>> +static struct clk_hw *s5_clk_hw_get(struct of_phandle_args *clkspec, void *data)
>> +{
>> + struct s5_clk_data *pll_clk = data;
>> + unsigned int idx = clkspec->args[0];
>> +
>> + if (idx >= N_CLOCKS) {
>> + pr_err("%s: invalid index %u\n", __func__, idx);
>> + return ERR_PTR(-EINVAL);
>> + }
>> +
>> + return &pll_clk->s5_hw[idx].hw;
>> +}
>> +
>> +static void __init s5_pll_init(struct device_node *np)
>> +{
>> + int i, ret;
>> + struct s5_clk_data *pll_clk;
>> + struct clk_init_data init = { 0 };
>
> Just do init = { } so that 0 doesn't trip up sparse.
I'm not sure what you mean by "trip up sparse", but its changed now.
>
>> +
>> + pll_clk = s5_clk_alloc(np);
>> + if (!pll_clk)
>> + return;
>> +
>> + init.ops = &s5_pll_ops;
>> + init.parent_names = NULL;
>> + init.num_parents = 0;
>
> Drop these last two lines if there aren't any parents.
>
OK.
>> +
>> + for (i = 0; i < N_CLOCKS; i++) {
>> + struct s5_hw_clk *s5_hw = &pll_clk->s5_hw[i];
>> +
>> + init.name = clk_names[i];
>> + s5_hw->index = i;
>> + s5_hw->reg = pll_clk->base + (i * sizeof(u32));
>> + s5_hw->hw.init = &init;
>> + ret = of_clk_hw_register(np, &s5_hw->hw);
>> + if (ret) {
>> + pr_err("failed to register %s clock\n", init.name);
>> + return;
>> + }
>> + }
>> +
>> + of_clk_add_hw_provider(np, s5_clk_hw_get, pll_clk);
>> +}
>> +CLK_OF_DECLARE_DRIVER(microchip_s5, "microchip,sparx5-dpll", s5_pll_init);
>
> Why DECLARE_DRIVER? Please add a comment indicating the other driver
> that is supposed to probe against this node. And is there any reason
> this can't be a platform driver? That is preferred over
> CLK_OF_DECLARE*() usage.
I will change it to a platform driver.
Thank you very much for your comments, they are highly appreciated.
---Lars
--
Lars Povlsen,
Microchip
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